HackStudio uses a TreeView to display the list of current variables
while debugging, and when the program completes, it sets that view's
model to a null model. This would trip an assertion if the TreeView
had something selected at the time, so this patch lessens the
assertion into a simple null check.
Additionally, the cursor would look laggy when moving about the
editor because the code was waiting for a window repaint to update
the cursor's look when it makes more sense to update the cursor
when it actually moves. This change also requires the base
GUI::TextEditor to expose a getter to tell if its currently in a drag
selection.
Finally, requesting a context menu in the line ruler on the side of
the editor would also place/remove breakpoints, which was counter
intuitive, so this requires a left click to modify breakpoint placement.