Use safe attribute accessor for RecentChange

The RecentChange does not guarantee that all attributes are populated.
Handily it provides a safe getter function in
RecentChange::getAttribute() that will return null with out triggering
an undefined index warning for missing attributes. Protects against log
spam like "Notice: Undefined index: rc_id".

Change-Id: Idee844f0d40a2a084e17f201b5e1501d59a0464d
(cherry picked from commit 78695ada64118461969f7a7b4ae0fec128505dd8)
Merge "Use safe attribute accessor for RecentChange" into wmf/1.24wmf21