Incorrect return value check in TextIndex.unindex

[morrison]

When you add a Category to a fresh install of Indico (as happens with the migration script), you run into a bug in TextIndex? that prevents you from proceeding. This line: ​https://indico-software.org/browser/indico/indico/MaKaC/common/indexes.py#L1206 checks whether IntStringMappedIndex?.getInteger has returned 0. The problem is that 0 is a legitimate value in the TextIndex? hash. If the index isn't found, getIndex returns None. I believe the line should read instead:

  if intId != None: