macosx: avoid out of bound exception which can occur while reading from log array

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>
(cherry picked from commit 2d81b923ef635a3336f127aa1530f4d3a1d5e18f)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/macosx/intf.m

@@ -1863,7 +1863,17 @@ unsigned int CocoaKeyToVLC( unichar i_key )
 
 - (id)tableView:(NSTableView *)aTableView objectValueForTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex
 {
-    return [o_msg_arr objectAtIndex: rowIndex];
+    NSMutableAttributedString *result = NULL;
+
+    [o_msg_lock lock];
+    if( rowIndex < [o_msg_arr count] )
+        result = [o_msg_arr objectAtIndex: rowIndex];
+    [o_msg_lock unlock];
+
+    if( result != NULL )
+        return result;
+    else
+        return @"";
 }
 
 - (void)processReceivedlibvlcMessage:(const msg_item_t *) item ofType: (int)i_type withStr: (char *)str