Fix: Exception when editing group name to same name from WebUI

If the user edits the group name in the Web UI, the "Rename Group"
button is enabled.  If the name is then edited back to its original
value, the button remains enabled.

If the user then submits the edit, an exception occurs:

  JdbcSQLException: Unique index or primary key violation

Add a check in the PutName REST view to prevent the rename from
being executed with the same name.  If the new name is the same,
just return it.

Change-Id: Ifba0ba646ee7895596cec22449abe8e2a466c375

gerrit-server/src/main/java/com/google/gerrit/server/group/PutName.java

@@ -55,9 +55,14 @@ public class PutName implements RestModifyView<GroupResource, Input> {
       throw new BadRequestException("name is required");
     }
 
+    final String newName = input.name.trim();
+    if (resource.toAccountGroup().getName().equals(newName)) {
+      return newName;
+    }
+
     try {
       return performRenameGroupFactory.create().renameGroup(
-          resource.toAccountGroup().getId(), input.name).group.getName();
+          resource.toAccountGroup().getId(), newName).group.getName();
     } catch (NoSuchGroupException e) {
       throw new ResourceNotFoundException();
     } catch (InvalidNameException e) {