Reject restoring change if its destination branch does not exist

If a branch got deleted and there was an abandoned change for this
branch, it was possible to restore this change.

Change-Id: I0b17b1b2e4d5cd97bcb1a8a06c3938626250666c
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/ProjectUtil.java

@@ -0,0 +1,48 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server;
+
+import com.google.gerrit.reviewdb.client.Branch;
+import com.google.gerrit.server.git.GitRepositoryManager;
+
+import org.eclipse.jgit.errors.RepositoryNotFoundException;
+import org.eclipse.jgit.lib.Repository;
+
+import java.io.IOException;
+
+public class ProjectUtil {
+
+  /**
+   * Checks whether the specified branch exists.
+   *
+   * @param repoManager Git repository manager to open the git repository
+   * @param branch the branch for which it should be checked if it exists
+   * @return <code>true</code> if the specified branch exists, otherwise
+   *         <code>false</code>
+   * @throws RepositoryNotFoundException the repository of the branch's project
+   *         does not exist.
+   * @throws IOException error while retrieving the branch from the repository.
+   */
+  public static boolean branchExists(final GitRepositoryManager repoManager,
+      final Branch.NameKey branch) throws RepositoryNotFoundException,
+      IOException {
+    final Repository repo = repoManager.openRepository(branch.getParentKey());
+    try {
+      return repo.getRef(branch.get()) != null;
+    } finally {
+      repo.close();
+    }
+  }
+}