Optimized query for detecting empty collections.

We don't actually need the detailed list of all _ID values; we're
simply interested in the count of items.

This change avoids misleading spam when logging.sh is enabled.

Bug: 159130154
Test: atest --test-mapping packages/providers/MediaProvider
Change-Id: I05b081db6e745e6cbc18c3d166ca1b1e50478cab
1 file changed