codereview: fix hg change on Windows

hg change fails on Windows with 'No valid patches found in output from hg diff'.

R=rsc
CC=golang-dev
https://golang.org/cl/4006043

diff --git a/lib/codereview/codereview.py b/lib/codereview/codereview.py
index 0a345d8f66f0eb633fb9e7a09d06c7380fd89c5d..ab8415e08742ec9ae5cd929d9cf689c61fcf9aa9 100644 (file)
--- a/lib/codereview/codereview.py
+++ b/lib/codereview/codereview.py
@@ -2607,7 +2607,7 @@ class MercurialVCS(VersionControlSystem):
                        self.base_rev = self.options.revision
                else:
                        mqparent, err = RunShellWithReturnCode(['hg', 'log', '--rev', 'qparent', '--template={node}'])
-                       if not err:
+                       if not err and mqparent != "":
                                self.base_rev = mqparent
                        else:
                                self.base_rev = RunShell(["hg", "parents", "-q"]).split(':')[1].strip()