Git: Fix soft assertion on Abort Rebase

When a rebase was initialized in a previous session or by
command-line.

Change-Id: I1a185f1bf1a9caeeba0d8358debc855cbd926d48
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/git/gitclient.cpp

@@ -2231,7 +2231,8 @@ GitClient::StashInfo &GitClient::stashInfo(const QString &workingDirectory)
 void GitClient::endStashScope(const QString &workingDirectory)
 {
     const QString repoDirectory = VcsManager::findTopLevelForDirectory(workingDirectory);
-    QTC_ASSERT(m_stashInfo.contains(repoDirectory), return);
+    if (!m_stashInfo.contains(repoDirectory))
+        return;
     m_stashInfo[repoDirectory].end();
 }