Fix unsupported operand type(s) for +: 'int' and 'str'

Change-Id: I88455107d63daaa60c3b33c010aa8c730a590c70

project.py

@@ -1601,7 +1601,7 @@ class Project(object):
 
       p = None
       try:
-        size = pos + r.headers.get('content-length', 0)
+        size = pos + int(r.headers.get('content-length', 0))
         unit = 1 << 10
 
         if size and not quiet: