Fix new page creation with selective serialization enabled

There is no point in retrieving an old revision for selective serialization if
we did not get an oldid passed in. This patch switches to full serialization
in that case without attempting to fetch the page source.

Error handlign in the getPageSrc helper is also slightly improved by checking
for the revision member first.

Change-Id: I2344e2106303c751a850fa9d296975dd844015d5
Merge "Fix new page creation with selective serialization enabled"