buildman: Deal nicely with invalid build-status file

The 'done' files created by buildman may end up being empty if buildman
runs out of disk space while writing them. This error is then persistent,
since even if disk space is reclaimed and the build retries, the empty
file causes an exception in the builder thread.

Deal with this silently by doing a rebuild.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/buildman/builderthread.py

@@ -156,7 +156,12 @@ class BuilderThread(threading.Thread):
         if result.already_done:
             # Get the return code from that build and use it
             with open(done_file, 'r') as fd:
-                result.return_code = int(fd.readline())
+                try:
+                    result.return_code = int(fd.readline())
+                except ValueError:
+                    # The file may be empty due to running out of disk space.
+                    # Try a rebuild
+                    result.return_code = RETURN_CODE_RETRY
 
             # Check the signal that the build needs to be retried
             if result.return_code == RETURN_CODE_RETRY: