Core: Fix QProcess::errorString() output

Fix regression introduced in commit 5147f73ac3.

Change-Id: I336e13d5127c5e6e2f9e7afdfa7956fc89533766
Reviewed-by: Marcel Krems <m.krems@software-vision.eu>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/io/qprocess.cpp

@@ -905,6 +905,7 @@ void QProcessPrivate::setError(QProcess::ProcessError error, const QString &desc
         switch (error) {
         case QProcess::FailedToStart:
             errorString = QProcess::tr("Process failed to start");
+            break;
         case QProcess::Crashed:
             errorString = QProcess::tr("Process crashed");
             break;