yocto-compat-layer.py: Fix trace when layers can't be processed

When all of the requested layers have unsatisfied dependencies, an error can occur. Check for the condition to avoid the traceback:

Traceback (most recent call last):
File "../scripts/yocto-compat-layer.py", line 203, in <module>
ret = main()
File "../scripts/yocto-compat-layer.py", line 194, in main
if not results[layer_name].wasSuccessful():
AttributeError: 'NoneType' object has no attribute 'wasSuccessful'

---
 scripts/yocto-compat-layer.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index a16974f..9a541c6 100755
@@ -191,7 +191,7 @@ def main():
         logger.info('')
         for layer_name in results_status:
             logger.info('%s ... %s' % (layer_name, results_status[layer_name]))
-            if not results[layer_name].wasSuccessful():
+            if not results[layer_name] or not results[layer_name].wasSuccessful():
                 ret = 2 # ret = 1 used for initialization errors
 
     cleanup_bblayers(None, None)

1.8.3.1