tweak error message

utils/pdfunite.cc

@@ -292,7 +292,7 @@ int main(int argc, char *argv[])
                 delete yRef;
                 delete countRef;
                 delete outStr;
-                error(errSyntaxError, -1, "XRef's Catalog is not a dictionary.");
+                error(errSyntaxError, -1, "PDFDoc::replacePageDict failed.");
                 return -1;
             }
             Ref *refPage = docs[i]->getCatalog()->getPageRef(j);