Fix calculation of project name if repo is not existing

The calculation of the project name in LocalDiskRepositoryManager
assumes that the relative path to the git repository ends with a
slash. This is only true if the repository exists in the file system.
If a project inherits from a non existing parent (the inheritFrom in
project.config points to a non existing parent), we try to lookup a
non existing repository. In this case the relative path is just the
project name without any '/' in the end. As result the code fails
with a StringIndexOutOfBoundsException.

Change-Id: Id48c0708d077a75adc6f9ab9dbd91d051959d43c
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/git/LocalDiskRepositoryManager.java

@@ -298,8 +298,11 @@ public class LocalDiskRepositoryManager implements GitRepositoryManager {
   }
 
   private Project.NameKey getProjectName(final File gitDir) {
-    final String relativeGitPath =
+    String relativeGitPath =
         getBasePath().toURI().relativize(gitDir.toURI()).getPath();
+    if (!relativeGitPath.endsWith("/")) {
+      relativeGitPath = relativeGitPath + "/";
+    }
     final String prefix =
         relativeGitPath.substring(0, relativeGitPath.length() - 1
             - gitDir.getName().length());