Fix a potential AttributeError when using ldap without fullName
Fix a potential AttributeError when using ldap without fullName

When an ldap server was configured without a fullName attribute assigned, it
would cause an AttributeError. Since having such a configuration is okay as long
as there are also sn and givenName attributes, we can just eat the
AttributeError.

Fixes bug 2382

1tush/reviewboard,1tush/reviewboard,chipx86/reviewboard,Khan/reviewboard,reviewboard/reviewboard,Khan/reviewboard,custode/reviewboard,1tush/reviewboard,atagar/ReviewBoard,brennie/reviewboard,custode/reviewboard,atagar/ReviewBoard,davidt/reviewboard,davidt/reviewboard,Khan/reviewboard,Khan/reviewboard,custode/reviewboard,Khan/reviewboard,KnowNo/reviewboard,Khan/reviewboard,beol/reviewboard,1tush/reviewboard,Khan/reviewboard,brennie/reviewboard,1tush/reviewboard,sgallagher/reviewboard,KnowNo/reviewboard,beol/reviewboard,Khan/reviewboard,reviewboard/reviewboard,atagar/ReviewBoard,sgallagher/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,davidt/reviewboard,atagar/ReviewBoard,atagar/ReviewBoard,bkochendorfer/reviewboard,beol/reviewboard,sgallagher/reviewboard,custode/reviewboard,chipx86/reviewboard,Khan/reviewboard,1tush/reviewboard,atagar/ReviewBoard,brennie/reviewboard,1tush/reviewboard,davidt/reviewboard,beol/reviewboard,chipx86/reviewboard,1tush/reviewboard,sgallagher/reviewboard,KnowNo/reviewboard,atagar/ReviewBoard,reviewboard/reviewboard,bkochendorfer/reviewboard,reviewboard/reviewboard,atagar/ReviewBoard,atagar/ReviewBoard,KnowNo/reviewboard,brennie/reviewboard,1tush/reviewboard,bkochendorfer/reviewboard