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: I94de7f5110bffe691c2f35df817b976dccc3c629
diff --git a/build/tools/repopick.py b/build/tools/repopick.py
index 41a31ba..2ce1ee7 100644
--- a/build/tools/repopick.py
+++ b/build/tools/repopick.py
@@ -291,7 +291,7 @@
 
         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)