Fixed assertion where painting a rectangular selection led to multiple layouts being checked out of the cache.
Fixed assertion where painting a rectangular selection led to
multiple layouts being checked out of the cache.

timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla