Update `agg_tiles_hash` docs and minor bug #1986

Job	Run time
Build aarch64-apple-darwin	16m 20s
Build aarch64-unknown-linux-gnu	12m 29s
Build debian-x86_64	8m 51s
Build x86_64-apple-darwin	12m 28s
Build x86_64-pc-windows-msvc	21m 24s
Build x86_64-unknown-linux-gnu	16m 17s
Build docker images	1m 19s
Test Legacy DB (postgis/postgis:11-3.0-alpine, postgres, disable)	10m 11s
Test Legacy DB (postgis/postgis:14-3.3-alpine, postgres, disable)	9m 41s
Test x86_64-apple-darwin	8m 57s
Test Legacy DB (postgis/postgis:15-3.3, postgres -c ssl=on -c ssl_cert_file=/etc/ssl/certs/ssl-ce...	11m 19s
Test x86_64-pc-windows-msvc	1m 51s
Test x86_64-unknown-linux-gnu	8m 6s
Package aarch64-apple-darwin	9s
Package aarch64-unknown-linux-gnu	10s
Package x86_64-apple-darwin	25s
Package x86_64-pc-windows-msvc	19s
Package x86_64-unknown-linux-gnu	6s
Package debian-x86_64	9s
CI Finished	3s
	2h 20m 34s

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