[pango/fix-attr-list-update: 1/2] Avoid unsigned int pitfalls

[Matthias Clasen <matthiasc src gnome org>]

commit 0e9dcc976b2a3f08f239d393f49ca2907cec099b
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun May 23 12:39:57 2021 -0400

    Avoid unsigned int pitfalls
    
    When we tried to catch attr list overflow in
    895759096309e7c, we overlooked that add - remove
    can be negative, leading to unexpected results.
    Avoid this case.
    
    Fixes: #561

 pango/pango-attributes.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/pango/pango-attributes.c b/pango/pango-attributes.c
index 63c031f9..f97892a6 100644
--- a/pango/pango-attributes.c
+++ b/pango/pango-attributes.c
@@ -1777,7 +1777,8 @@ pango_attr_list_update (PangoAttrList *list,
           }
         else if (attr->end_index >= pos + remove)
           {
-            if (G_MAXUINT - attr->end_index < add - remove)
+            if (add > remove &&
+                G_MAXUINT - attr->end_index < add - remove)
               attr->end_index = G_MAXUINT;
             else
               attr->end_index += add - remove;