Bug 17933 - Internal software error when searching patron without birth date

Bug 17933 - Internal software error when searching patron without birth date

When patrons don't have date of birth (which is not required) patron
search results on moremember page produce internal server error since we
can't convert MySQL invalid date 0000-00-00 to datetime object and
call strfdate on it.

Additionally, since we assign dates to template variables and after
than assign whole $data hash to template, later assigment overrides
previous one, so we see birth date field even for patrons which don't
have one.

This patch fixes both of those problems.

Test:
1. edit patron and remove it's birth date
2. try to search for it, and verify server error
3. apply patch
4. repeat search for patron and verify that it works and doesn't
   have enpty birth date field

Signed-off-by: Grace McKenzie <grace.mcky@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>