[sidePanelWidth]: Runtime error when value is 1.0

**Describe the bug**
When `sidePanelWidth` is set to 1.0, focusing preview window causes a runtime error

**To Reproduce**
Steps to reproduce the behavior:

https://github.com/user-attachments/assets/4cfd7de6-cfdc-4463-8f4a-10fbd798c659

1. Set config option `sidePanelWidth` to 1.0
2. Relaunch `lazygit`, your 1-5 windows should take full width now
3. Press + key, which should display the preview window on the right that you normally see, when `sidePanelWidth` has default value
4. Select Commits window (number 4), press Enter on any commit and Enter again on any file in the commit
5. Runtime error happens

**Expected behavior**

https://github.com/user-attachments/assets/7f7bfab8-4c9b-404d-af02-396647cc344f

Preview window should be focused as expected

**Version info:**
commit=66caa25dcd4c247589e6adc71a6bc088678f3212, build date=2025-05-03T02:30:12Z, build source=binaryRelease, version=0.50.0, os=darwin, arch=arm64, git version=2.49.0

git version 2.49.0

**Additional context**

Error trace

panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/jesseduffield/lazycore/pkg/boxlayout.normalizeWeights({0x14000aff9f0, 0x2, 0x2})
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/lazycore/pkg/boxlayout/boxlayout.go:161 +0x3d0
github.com/jesseduffield/lazycore/pkg/boxlayout.calcSizes({0x14000c385b0, 0x2, 0x14000f4ac78?}, 0x8d)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/lazycore/pkg/boxlayout/boxlayout.go:97 +0x6c
github.com/jesseduffield/lazycore/pkg/boxlayout.ArrangeWindows(0x14000c08280, 0x0, 0x0, 0x8d, 0x26)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/lazycore/pkg/boxlayout/boxlayout.go:75 +0xe0
github.com/jesseduffield/lazycore/pkg/boxlayout.ArrangeWindows(0x14000f4b090, 0x0, 0x0, 0x8d, 0x27)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/lazycore/pkg/boxlayout/boxlayout.go:86 +0x24c
github.com/jesseduffield/lazygit/pkg/gui/controllers/helpers.GetWindowDimensions({0x8d, 0x27, 0x1400021f008, {0x100a73e7e, 0x4}, {0x100a73e7e, 0x4}, {0x100a760e5, 0x5}, 0x0, ...})
/home/runner/work/lazygit/lazygit/pkg/gui/controllers/helpers/window_arrangement_helper.go:168 +0x438
github.com/jesseduffield/lazygit/pkg/gui/controllers/helpers.(*WindowArrangementHelper).GetWindowDimensions(0x14000542100, {0x14000a30370, 0xa5}, {0x0, 0x0})
/home/runner/work/lazygit/lazygit/pkg/gui/controllers/helpers/window_arrangement_helper.go:106 +0x308
github.com/jesseduffield/lazygit/pkg/gui.(*Gui).getWindowDimensions(...)
/home/runner/work/lazygit/lazygit/pkg/gui/gui.go:1134
github.com/jesseduffield/lazygit/pkg/gui.(*Gui).layout(0x14000240308, 0x14000270000)
/home/runner/work/lazygit/lazygit/pkg/gui/layout.go:26 +0x10c
github.com/jesseduffield/gocui.ManagerFunc.Layout(0x0?, 0x140017990a0?)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/gocui/gui.go:728 +0x28
github.com/jesseduffield/gocui.(*Gui).flush(0x14000270000)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/gocui/gui.go:1185 +0xac
github.com/jesseduffield/gocui.(*Gui).processEvent(0x14000270000)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/gocui/gui.go:813 +0x208
github.com/jesseduffield/gocui.(*Gui).MainLoop(0x14000270000)
/home/runner/work/lazygit/lazygit/vendor/github.com/jesseduffield/gocui/gui.go:778 +0x108
github.com/jesseduffield/lazygit/pkg/gui.(*Gui).Run(0x14000240308, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}})
/home/runner/work/lazygit/lazygit/pkg/gui/gui.go:867 +0x434
github.com/jesseduffield/lazygit/pkg/gui.(*Gui).RunAndHandleError.func1()
/home/runner/work/lazygit/lazygit/pkg/gui/gui.go:873 +0x48
github.com/jesseduffield/lazygit/pkg/utils.SafeWithError(0x14000043928?)
/home/runner/work/lazygit/lazygit/pkg/utils/utils.go:90 +0x5c
github.com/jesseduffield/lazygit/pkg/gui.(*Gui).RunAndHandleError(0x14000240308, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}})
/home/runner/work/lazygit/lazygit/pkg/gui/gui.go:872 +0xc4
github.com/jesseduffield/lazygit/pkg/app.(*App).Run(...)
/home/runner/work/lazygit/lazygit/pkg/app/app.go:270
github.com/jesseduffield/lazygit/pkg/app.Run({0x100e6bfb8?, 0x140000cc6e0?}, 0x140001f71c0, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, ...}})
/home/runner/work/lazygit/lazygit/pkg/app/app.go:48 +0xb0
github.com/jesseduffield/lazygit/pkg/app.Start(0x14000043ef8, {0x0, 0x0})
/home/runner/work/lazygit/lazygit/pkg/app/entry_point.go:168 +0x9b0
main.main()
/home/runner/work/lazygit/lazygit/main.go:23 +0x98