NotificationEmail: Fix eliding project name without slash

When a project name does not contain a slash, the name should not
be elided with "...".

Add extra tests that would have caught this.

Bug: Issue 10896
Change-Id: I131fa5c5016e758e8c6d7d2b09625fae6593da7b

java/com/google/gerrit/server/mail/send/NotificationEmail.java

@@ -132,6 +132,9 @@ public abstract class NotificationEmail extends OutgoingEmail {
     if (lastIndexSlash == 0) {
       return projectName.substring(1); // Remove the first slash
     }
+    if (lastIndexSlash == -1) { // No slash in the project name
+      return projectName;
+    }
 
     return "..." + projectName.substring(lastIndexSlash + 1);
   }