repopick: Ignore the trailing slash in change numbers

Trailing slashes cause 'patchset' to be an empty string, which
cannot be converted to an int. If we have a trailing slash, ignore
it and pick the current patchset.

Change-Id: Ifad60b7f6ff3dcfd9dd80b2e93b1f909aa360666

build/tools/repopick.py

@@ -306,7 +306,7 @@ if __name__ == '__main__':
 
         change = int(change)
 
-        if patchset is not None:
+        if patchset:
             patchset = int(patchset)
 
         review = next((x for x in reviews if x['number'] == change), None)