fdo#47689: Avoid crashing mdworker: Don't use uninitialized variable

It's the isCustom field that should be checked to see whether the
customAttribute field has been assigned or not.

Change-Id: I5d2af26b675ab0cbc0e1844eb98ebaf5145eb73d

extensions/source/macosx/spotlight/OOoMetaDataParser.m

@@ -172,7 +172,7 @@ static NSDictionary *metaXML2MDIKeys;
         }
         // cleanup part 1
         [textCurrentElement release];
-        if (customAttribute != nil) {
+        if (isCustom == YES) {
             [customAttribute release];
         }
     }