CMFActivity: Fix ActivityRuntimeEnvironment.getPriority when activity was not...

CMFActivity: Fix ActivityRuntimeEnvironment.getPriority when activity was not loaded from an SQL queue.

This happens when activities are being flushed from the ActivityBuffer
directly, without being inserted into and then loaded from the SQL queue.
It is unclear whether there are uses of this pattern besides
testCMFActivity, but it is easy enough to fix.

product/CMFActivity/ActivityRuntimeEnvironment.py

@@ -61,7 +61,11 @@ class ActivityRuntimeEnvironment(object):
   def getPriority(self):
     result = self._priority
     if result is None:
-      return self._message.line.priority
+      message = self._message
+      line = message.line
+      if line is None:
+        return message.activity_kw.get('priority', 1)
+      return line.priority
     return result
 
   security.declarePublic('edit')

product/CMFActivity/ActivityTool.py

@@ -197,6 +197,7 @@ class Message(BaseMessage):
   traceback = None
   document_uid = None
   is_registered = False
+  line = None
 
   def __init__(
       self,