[Regression] Can only copy from file diff when selecting with Ctrl-a

[Doodeletion]

I can only copy from file diff view when using Ctrl-a to select everything. Both Ctrl-c and right click > copy work then.

I cannot copy when selecting lines with mouse/keyboard, neither with Ctrl-c nor with right click > copy.

I think this might be a regression related to #924.

[gadfly3173]

I think this is a Linux specific problem, sometimes copy text would not work.

[Doodeletion]

I found the issue, will explain in a few minutes.

[Doodeletion]

The issue is that when selecting text from the bottom to the top, Selection.StartPosition will not be the top of the selection, but the bottom, where the selection started.