[mutter/gnome-3-34] x11: Iterate over selections in a safer manner for event handling

[Carlos Garnacho <carlosg src gnome org>]

commit 156dd576f446b8358fc477a58425b616e4196fc8
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Oct 21 12:58:35 2019 +0200

    x11: Iterate over selections in a safer manner for event handling
    
    It might be the case that handling an event induces the stream to
    trigger completion, hence removing itself from the list. In that
    case we would operate on the no longer valid list element to fetch
    the next one.
    
    Keep a pointer to the next element beforehand, so we can tiptoe
    over streams that did remove themselves.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/869
    (cherry picked from commit 45a8806e652346523cb66fb4777e15b63aa90c2a)

 src/x11/events.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)
---
diff --git a/src/x11/events.c b/src/x11/events.c
index 7fc7e3bf9..95cc714d0 100644
--- a/src/x11/events.c
+++ b/src/x11/events.c
@@ -1734,11 +1734,21 @@ process_selection_event (MetaX11Display *x11_display,
 
   handled |= meta_x11_selection_handle_event (x11_display, event);
 
-  for (l = x11_display->selection.input_streams; l && !handled; l = l->next)
-    handled |= meta_x11_selection_input_stream_xevent (l->data, event);
+  for (l = x11_display->selection.input_streams; l && !handled;)
+    {
+      GList *next = l->next;
+
+      handled |= meta_x11_selection_input_stream_xevent (l->data, event);
+      l = next;
+    }
 
-  for (l = x11_display->selection.output_streams; l && !handled; l = l->next)
-    handled |= meta_x11_selection_output_stream_xevent (l->data, event);
+  for (l = x11_display->selection.output_streams; l && !handled;)
+    {
+      GList *next = l->next;
+
+      handled |= meta_x11_selection_output_stream_xevent (l->data, event);
+      l = next;
+    }
 
   return handled;
 }