bitbake: bitbake: cache: Fix error when cache is rebuilt

It is expected that load_cachfile() returns an integer indicating how
many entries were loaded from the cache. In the event the cache needs to
be rebuilt, 0 must be returned to prevent python from attempting to add
an None and an integer together.

(Bitbake rev: 3459d98fbc280637ecb36961bda8436818ee51e5)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cache.py

@@ -464,14 +464,14 @@ class Cache(NoCache):
                     bitbake_ver = pickled.load()
                 except Exception:
                     self.logger.info('Invalid cache, rebuilding...')
-                    return
+                    return 0
 
                 if cache_ver != __cache_version__:
                     self.logger.info('Cache version mismatch, rebuilding...')
-                    return
+                    return 0
                 elif bitbake_ver != bb.__version__:
                     self.logger.info('Bitbake version mismatch, rebuilding...')
-                    return
+                    return 0
 
                 # Load the rest of the cache file
                 current_progress = 0