Make sure all pattern args get cleared when parsing a new pattern

The user can call qSetMessagePattern after program start, so we need to
be sure that the parsed argument data is properly cleared.

Task-number: QTBUG-57144
Change-Id: I1978c6b95bd84639a8c4fffd1487429b04725522
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

src/corelib/global/qlogging.cpp

@@ -1039,6 +1039,10 @@ void QMessagePattern::setPattern(const QString &pattern)
         delete [] literals;
     }
     delete [] tokens;
+    timeArgs.clear();
+#ifdef QLOGGING_HAVE_BACKTRACE
+    backtraceArgs.clear();
+#endif
 
     // scanner
     QList<QString> lexemes;