LP#1298985: Protect against bad summary types

LP#1298985: Protect against bad summary types

Ensure that if we are asked for summary information in Patron Information that
we have any form of definition for it *and* we have code to call. If neither
case is true pretend they didn't ask for any to begin with.

Testing notes
-------------
Here is an example of the sort of request that, prior to this patch,
could cause a SIPServer backend to crash:

6300020150615    111700      Y   AOUinst|AAuser|

Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>