Fix use after free in interface handler

ASAN reported a use after free in after rB15d78ea85b602c. This commit
removed a reassignment of the `data` variable here that was actually
required because it may have been freed earlier in the function. This
sort of error would be avoided if the same variable wasn't reused for
different purposes.

source/blender/editors/interface/interface_handlers.c

@@ -7693,6 +7693,7 @@ static int ui_do_button(bContext *C, uiBlock *block, uiBut *but, const wmEvent *
   }
 
 #ifdef USE_DRAG_MULTINUM
+  data = but->active;
   if (data) {
     if (ELEM(event->type, MOUSEMOVE, INBETWEEN_MOUSEMOVE) ||
         /* if we started dragging, progress on any event */