Fix T44011: Ruler/Knife/Loop-cut fail in quad-view

This is a kind of sloppy-focus,
resolving long standing bug with loop-cut/knife/ruler /w quad-view.

Where activating a tool would lock onto one of quad-views,
especially problematic when activating from the toolbar or menus.

source/blender/windowmanager/wm_event_system.h

@@ -56,6 +56,7 @@ typedef struct wmEventHandler {
 	wmOperator *op;                     /* for derived/modal handlers */
 	struct ScrArea *op_area;            /* for derived/modal handlers */
 	struct ARegion *op_region;          /* for derived/modal handlers */
+	short           op_region_type;     /* for derived/modal handlers */
 
 	/* ui handler */
 	wmUIHandlerFunc ui_handle;          /* callback receiving events */