Exception when LDAP parsing fails

[bugch3ck]

Caught this exception while running basic tests.

Exception happened during processing of request from ('192.168.0.185', 57566)
Traceback (most recent call last):
  File "/usr/lib/python2.7/SocketServer.py", line 593, in process_request_thread
    self.finish_request(request, client_address)
  File "/usr/lib/python2.7/SocketServer.py", line 334, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python2.7/SocketServer.py", line 649, in __init__
    self.handle()
  File "/root/imposter/src/msldap_server.py", line 35, in handle
    req = ldap_request_parse(data)
  File "/root/imposter/src/msldap_utils.py", line 11, in ldap_request_parse
    msg = decoder.decode(data, asn1Spec=LDAPMessage())[0]
  File "/usr/lib/python2.7/dist-packages/pyasn1/codec/ber/decoder.py", line 560, in __call__
    'Short octet stream on tag decoding'
SubstrateUnderrunError: Short octet stream on tag decoding

Fix exception handling when parsing LDAP messages.