UI difference in Composite after migrating eclipse based application from version 4.15 to 4.26

Let's make sure issue is not already fixed in latest builds first.

- [x] I verified I can reproduce this issue against [latest Integration Build of Eclipse SDK](https://download.eclipse.org/eclipse/downloads/)

## Steps to reproduce

We have migrated our eclipse based application from eclipse 4.15 to eclipse 4.26, and while testing the application we found an UI difference in composite.
We have able to see the slant line from bottom right hand side corner. The UI is not rendered properly.

We are able to see for all the Composites which are not selected.

When we click on one of the composite, then these issue is not seen. Seems like coolbar is visible for these and which overrides the slant lines/issue

Also, we are getting null pointer exception

I expected: *< No change in UI>*

But got: **

## Here is some relevant log output

From `org.eclipse.e4.ui.workbench

```
!ENTRY org.eclipse.e4.ui.workbench 4 0 2025-02-25 11:41:40.629
!MESSAGE An exception occurred while notifying part listeners
!STACK 0
java.lang.NullPointerException: Cannot read field "layout" because "this" is null
at org.eclipse.swt.widgets.Composite.markLayout(Composite.java:861)
at org.eclipse.swt.widgets.Composite.layout(Composite.java:824)
at org.eclipse.swt.widgets.Control.requestLayout(Control.java:2398)
at org.eclipse.ui.internal.CoolBarToTrimManager.update(CoolBarToTrimManager.java:602)
at org.eclipse.ui.internal.WorkbenchWindow.updateActionBars(WorkbenchWindow.java:2492)
at org.eclipse.ui.internal.WorkbenchPage.updateActionBars(WorkbenchPage.java:4334)
at org.eclipse.ui.internal.WorkbenchPage$ActionSwitcher.updateActivePart(WorkbenchPage.java:668)
at org.eclipse.ui.internal.WorkbenchPage.updateActivations(WorkbenchPage.java:331)
at org.eclipse.ui.internal.WorkbenchPage$E4PartListener.partActivated(WorkbenchPage.java:212)
at org.eclipse.e4.ui.internal.workbench.PartServiceImpl$2.run(PartServiceImpl.java:250)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.firePartActivated(PartServiceImpl.java:247)
at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:774)
at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:683)
at org.eclipse.e4.ui.internal.workbench.swt.AbstractPartRenderer.activate(AbstractPartRenderer.java:97)
at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer.lambda$3(StackRenderer.java:963)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4256)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1066)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1090)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1075)
at org.eclipse.swt.widgets.Shell.setActiveControl(Shell.java:1530)
at org.eclipse.swt.widgets.Shell.WM_MOUSEACTIVATE(Shell.java:2441)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4787)
at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:340)
at org.eclipse.swt.widgets.Decorations.windowProc(Decorations.java:1478)
at org.eclipse.swt.widgets.Shell.windowProc(Shell.java:2284)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
```

## Tested under this environment:
* OS & version: MS windows 10
* Eclipse IDE/Platform version (as shown in *Help > About*): Eclipse 4.26
*

In First Photo, third composite is selected, no issue is seen. Issue is seen in first two parts.
In Second Photo, second composite is selected, so no issue is seen. Issue is seen in first and last parts.

## Community

- [x] I understand reporting an issue to this OSS project does not mandate anyone to fix it. Other contributors may consider the issue, or not, at their own convenience. The most efficient way to get it fixed is that I fix it myself and contribute it back as a good quality patch to the project.