Open debugger at assert location from the GUI assert handler too

This should have been part of 55fd62c1e3
which only updated the default assert handler, but not the one used by
default in all GUI applications, for some reason, see there for more
explanations.

Do this now to ensure that after pressing "Yes" in the assert failure
dialog, the debugger opens at the assert location and not deep inside
wxWidgets code.

See #11184.

src/common/appcmn.cpp

@@ -489,7 +489,9 @@ bool wxGUIAppTraitsBase::ShowAssertDialog(const wxString& msg)
                               wxYES_NO | wxCANCEL | wxICON_STOP ) )
         {
             case wxYES:
-                wxTrap();
+                // See the comment about using the same variable in
+                // DoShowAssertDialog().
+                wxTrapInAssert = true;
                 break;
 
             case wxCANCEL: