Hi,
this patch is about fixing a bug in GtkTextView that prevents the current text selection to be extended by moving the mouse scrollwheel (with the mouse left button pressed).


Steps to reproduce:
1. Open a sufficient large text file so it can be scrolled (eg. some C file).
2. Scroll the view to somewhere in the middle of the file
3. With mouse left button do a click and keep it pressed, then move the mouse scrollwheel to start selecting text from the place you clicked.

Expected results:
Text should be selected to the mouse pointer position as we scroll the view with the scrollwheel.

Actual results:
None text is selected, and the view does not scroll past the current viewport.

Note that if we move the mouse a little while doing this (ie. we provoke a motion_notify event) then the text selection works as expected, but just using the mouse scrollwheel alone does not.