crop: Clamp cursor when updating crop zone state

A continuation of 000fbe8 as occivink/mpv-scripts#67 was updated.

Author: dexeonify

scripts/crop.lua

@@ -314,6 +314,7 @@ function update_crop_zone_state()
         cancel_crop()
         return
     end
+    cursor = clamp_point(cursor, dim)
     if crop_first_corner == nil then
         crop_first_corner = screen_to_video_norm(cursor, dim)
         redraw()