fixed crash on unknown PDU reporting

CHANGES.txt

@@ -8,6 +8,8 @@ Revision 4.3.5, released 2017-0X-XX
   SNMPv1 PDU
 - Fix to possible infinite recursion in TextualConvention.prettyIn()
 - TextualConvention is now a new-style class
+- Fixed crash when attempting to report unsupported request/notification
+  PDU back to sender
 
 Revision 4.3.4, released 2017-03-01
 -----------------------------------

pysnmp/proto/rfc3412.py

@@ -361,8 +361,6 @@ class MsgAndPduDispatcher(object):
 
                 debug.logger & debug.flagDsp and debug.logger('receiveMessage: unhandled PDU type')
 
-                # XXX fails on unknown PDU
-
                 try:
                     (destTransportDomain,
                      destTransportAddress,
@@ -374,7 +372,7 @@ class MsgAndPduDispatcher(object):
                         statusInformation
                     )
 
-                except error.StatusInformation:
+                except (error.StatusInformation, error.ProtocolError):
                     debug.logger & debug.flagDsp and debug.logger(
                         'receiveMessage: report failed, statusInformation %s' % sys.exc_info()[1])
                     return restOfWholeMsg