BF: Allow to remove a submodule with a remote without refs

Author: yarikoptic

Diff for: git/objects/submodule/base.py

@@ -836,7 +836,7 @@ def remove(self, module=True, force=False, configuration=True, dry_run=False):
                         num_branches_with_new_commits += len(mod.git.cherry(rref)) != 0
                     # END for each remote ref
                     # not a single remote branch contained all our commits
-                    if num_branches_with_new_commits == len(rrefs):
+                    if len(rrefs) and num_branches_with_new_commits == len(rrefs):
                         raise InvalidGitRepositoryError(
                             "Cannot delete module at %s as there are new commits" % mod.working_tree_dir)
                     # END handle new commits