VCS: Never try to run empty binaries

Never try to run empty binaries.

Task-number: QTCREATORBUG-6849
Change-Id: I591fdb9d39394fc8097908f5934a1a96518859cb
Reviewed-by: Hugues Delorme <delorme.hugues@fougsys.fr>

src/plugins/git/gitclient.cpp

@@ -2329,6 +2329,9 @@ QString GitClient::gitVersionString(bool silent, QString *errorMessage) const
 // determine version as '(major << 16) + (minor << 8) + patch' or 0.
 unsigned GitClient::synchronousGitVersion(bool silent, QString *errorMessage) const
 {
+    if (gitBinaryPath().isEmpty())
+        return 0;
+
     // run git --version
     QByteArray outputText;
     QByteArray errorText;