safety fix in case code incorrectly tries to use the reuslt of forwarding a method to the undo manager.

ChangeLog

@@ -1,4 +1,10 @@
+2024-10-29 Richard Frith-Macdonald <rfm@gnu.org>
+
+	* Source/NSUndoManager.m: set zero/nil return value when forwarding
+	invocation ... in case calling code tries to use the result.
+
 2024-10-28 Hugo Melder <hugo@algoriddim.com>
+
 	* Source/NSString.m:
 	-commonPrefixWithString:options: returns nil when string supplied as
 	first argument is nil. On macOS, the empty string is returned instead.

Source/NSUndoManager.m

@@ -429,6 +429,11 @@
  */
 - (void) forwardInvocation: (NSInvocation*)anInvocation
 {
+  NSUInteger    size = [[anInvocation methodSignature] methodReturnLength];
+  unsigned char v[size];
+
+  memset(v, '\0', size);
+
   if (_disableCount == 0)
     {
       if (_nextTarget == nil)
@@ -466,6 +471,8 @@
 	  _runLoopGroupingPending = YES;
 	}
     }
+
+  [anInvocation setReturnValue: (void*)v];
 }
 
 /**