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
diff --git a/build/tools/repopick.py b/build/tools/repopick.py
index 248f2d7..a620f3b 100755
--- a/build/tools/repopick.py
+++ b/build/tools/repopick.py
@@ -306,7 +306,7 @@
 
         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)