Don't prune variable-depth children while a minzoom-gated feature is pending
The minzoom_feature_pending flag from #397 keeps a variable-depth pyramid
subdividing until explicit per-feature minzooms are satisfied, but two gaps
let features still be dropped:
The flag was only set when tippecanoe_minzoom > z + 1, so a feature whose
minzoom is exactly z + 1 never marked the tile pending, even though a leaf
at z carries only z-visible content.
The early-stop commit never consulted the flag: a tile that succeeded in
stopping early inserted itself into skip_children_out unconditionally,
pruning the children the pending feature needed. The flag only inflated
estimated_complexity_out, which the pruning ignores.
Set the flag for any feature excluded below its minzoom, include it in the
early-stop veto, and skip child pruning while it is set. Adds a fixture
covering the minzoom == z + 1 boundary; make test passes with no diffs to
existing fixtures.
Brandon Keepers
0badb242be