Fixed missing return statement in Mercurial.controls_location(), it

only got found after reverting `VersionControl.controls_location()`

src/pip/_internal/vcs/mercurial.py

@@ -147,6 +147,7 @@ def controls_location(cls, location):
                 show_stdout=False,
                 on_returncode='raise',
                 log_failed_cmd=False)
+            return True
         except (BadCommand, InstallationError):
             return False