Bug 16285 - write_age() function throws error for patron categories that don't include dateofbirth in form

To test:
1 Add a patron in category Library or School
2 Note the js error in the console
3 Apply patch
4 Repeat and note the error is gone

Signed-off-by: Chris Cormack <chrisc@catalyst.net.z>

Made it an explicit if, and fixed the author of the commit

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

Signed-off-by: Brendan Gallagher <bredan@bywatersolutions.com>

koha-tmpl/intranet-tmpl/prog/en/modules/members/memberentrygen.tt

@@ -18,7 +18,9 @@ $(document).ready(function() {
 	[% END %]
 	$("#dateofbirth").datepicker({ maxDate: "-1D", yearRange: "c-120:" });
 	dateformat = $("#dateofbirth").siblings(".hint").first().html();
-	write_age();
+    if( $('#dateofbirth').length ) {
+        write_age();
+    }
 	$("#entryform").validate({
 		rules: {
 			email: {