Filters are in conflict when their combination is guaranteed
to return no results. For instance: minor and log entries
is a conflict because major/minor does not apply to
log entries and the field is set to major by default.
Letting conflicts go through result in some very slow
database queries.
Bug: T160220
Change-Id: Ia6b0125c675c4a3cc4e4be4f83d1bd10d23059ba