Original ImageJ logic gets invoked in pure ImageJ2 GUI mode

Launch ImageJ2 via:
```
mvn -Pexec -Dscijava.ui=swing
```
When the ImageJ2 GUI comes up, choose _Process → Image Calculator..._ from the menu.

An original ImageJ dialog box appears with title "No Image" and message "There are no images open"

This is surprising—is the wrong "Image Calculator..." command executing? Or is ImageJ's active image logic being triggered indirectly somehow during execution of the ImageJ2 command `net.imagej.plugins.commands.calculator.ImageCalculator`? The menu item has the puzzle piece icon, indicating it's a SciJava/ImageJ2 command, so if the original ImageJ command is actually what runs when the menu item is clicked, that's :exploding_head:. But it's also :exploding_head: if original ImageJ's active image logic is somehow triggering from the ImageJ2 command code... :shrug:

Reproduce the issue with `mvn -Pexec -Dscijava.ui=swing`, then start from `net.imagej.plugins.commands.calculator.ImageCalculator` and trace what runs when Process → Image Calculator is selected. Determine whether the original ImageJ dialog is invoked by the ImageJ2 command or by another path; done means the invocation source is identified and pure ImageJ2 mode behaves correctly.

Written by the indexing model from the issue text.