#1806: if there is nothing left after removing the exclude region (vi…

…deo region) then stop and avoid an error when trying to merge an empty list of rectangles

git-svn-id: https://xpra.org/svn/Xpra/trunk@19020 3bb7dfac-3a0b-4e04-842a-767bc560f471

src/xpra/server/window/window_source.py

@@ -1443,7 +1443,10 @@ def send_full_window_update():
                     #better, so replace with merged regions:
                     regions = merged_rects
 
-            if len(regions)==1:
+            if not regions:
+                #nothing left after removing the exclude region
+                return
+            elif len(regions)==1:
                 merged = regions[0]
             else:
                 merged = merge_all(regions)