vercmp: don't choke on empty first version components

(Bitbake rev: e75aa94e9477933c5a40021b2a8e844db54f29da)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/lib/bb/utils.py

@@ -93,7 +93,7 @@ def vercmp(ta, tb):
     (ea, va, ra) = ta
     (eb, vb, rb) = tb
 
-    r = int(ea)-int(eb)
+    r = int(ea or 0) - int(eb or 0)
     if (r == 0):
         r = vercmp_part(va, vb)
     if (r == 0):