API: DWIM for action=edit&section=new&appendtext=...

While it doesn't make a whole lot of sense to prepend or append with
section=new, the user certainly doesn't intend to be copying the
contents of section 0. In the spirit of "do what I mean", we should
probably prepend/append to empty text in this situation.

Bug: 52538
Change-Id: I9b03635906ca665a4f68b3bd35d05ae9108e2356
Merge "API: DWIM for action=edit&section=new&appendtext=..."