De-pessimize QTlsBackendOpenSSL::clearErrorQueue()

We don't need to format the error messages into a QString just to
clear the error queue. Just looping over q_ERR_get_error() does the
trick, too, and isn't less readable.

Pick-to: 6.3
Change-Id: Idc42f8c4ae4374d952cb357fca6c0fca0e04d086
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/plugins/tls/openssl/qtlsbackend_openssl.cpp

@@ -86,8 +86,8 @@ void QTlsBackendOpenSSL::logAndClearErrorQueue()
 
 void QTlsBackendOpenSSL::clearErrorQueue()
 {
-    const auto errs = getErrorsFromOpenSsl();
-    Q_UNUSED(errs);
+    while (q_ERR_get_error())
+        ;
 }
 
 bool QTlsBackendOpenSSL::ensureLibraryLoaded()