devtool/standard: Fix lock in _prep_extract_operation

If for any reason the parse_recipe fail in extract command the process gets locked because Cooker is expecting the finish event by tinfoil.

For example:

$ devtool extract remake /tmp/remake

ERROR: remake is unavailable:
remake was skipped: PREFERRED_PROVIDER_virtual/make set to make, not remake

---
 scripts/lib/devtool/standard.py | 1 +
 1 file changed, 1 insertion(+)

index 5ff1e23..5fa1317 100644
@@ -436,6 +436,7 @@ def _prep_extract_operation(config, basepath, recipename, tinfoil=None):
 
     rd = parse_recipe(config, tinfoil, recipename, True)
     if not rd:
+        tinfoil.shutdown()
         return None
 
     if bb.data.inherits_class('kernel-yocto', rd):

2.1.4