fix(googlereader): raise item IDs limit to 10000

Since fbbff63f, a non-positive limit is clamped to model.MaxEntryLimit
instead of producing an unbounded query. /stream/items/ids defaults "n"
to 0, so omitting it started returning at most 1000 IDs, whereas
previous versions returned every matching entry.

Cap the four ID stream handlers at model.MaxEntryIDsLimit instead, like
the REST API does for /v1/entries/ids: ID lists are cheap, and clients
can still follow the continuation offset for the remainder.

Fixes: #4479