macosx: fixed crash in case either psz_module or psz_msg are NULL when received from core

Fixes playback of AVI files... ;)

modules/gui/macosx/intf.m

@@ -158,13 +158,14 @@ static void MsgCallback( msg_cb_data_t *data, msg_item_t *item, unsigned int i )
     int canc = vlc_savecancel();
     NSAutoreleasePool * o_pool = [[NSAutoreleasePool alloc] init];
 
-    NSDictionary *o_dict = [NSDictionary dictionaryWithObjects: 
-                            [NSArray arrayWithObjects: 
-                             [NSString stringWithUTF8String: item->psz_module],
-                             [NSString stringWithUTF8String: item->psz_msg],
-                             [NSNumber numberWithInt: item->i_type], nil] 
-                                                       forKeys:
-                            [NSArray arrayWithObjects: @"Module", @"Message", @"Type", nil]];
+    /* this may happen from time to time, let's bail out as info would be useless anyway */ 
+    if( !item->psz_module || !item->psz_msg )
+        return;
+
+    NSDictionary *o_dict = [NSDictionary dictionaryWithObjectsAndKeys:
+                                [NSString stringWithUTF8String: item->psz_module], @"Module",
+                                [NSString stringWithUTF8String: item->psz_msg], @"Message",
+                                [NSNumber numberWithInt: item->i_type], @"Type", nil];
 
     [[NSNotificationCenter defaultCenter] postNotificationName: @"VLCCoreMessageReceived" 
                                                         object: nil