API: Fix a bug to make list=allfileusages functional again

Querying list=allfileusages with affrom, afto, or afunique
will always get afinvalidtitle because the code passes the namespace
wrongly due to gerrit Iaa5a71ec. This patch fixes the problem.

Change-Id: I010dc3a03be74f49902fd446e7dbc306c16b869c
Merge "API: Fix a bug to make list=allfileusages functional again"