Ensure that interaction ends, once begun.

Wrap in try-finally.

Cherry-pick c73dfcd1 from master.

src/ZPublisher/WSGIPublisher.py

@@ -167,6 +167,7 @@ def publish(request, module_name,
 
     notify(PubStart(request))
     newInteraction()
+    try:
         request.processInputs()
         response = request.response
 
@@ -206,7 +207,7 @@ def publish(request, module_name,
 
         if result is not response:
             response.setBody(result)
-
+    finally:
         endInteraction()
 
     notify(PubBeforeCommit(request))