refactor: fix `Forge::processIndexes()` for empty `$this->fields` (#9… #12648

Job	Run time
Setup PHP Version for Code Coverage	1s
Others (8.3) / Sanity Tests	2m 39s
Others (8.2) / Sanity Tests	3m 46s
Others (8.1) / Sanity Tests	2m 28s
DatabaseLive (8.1, MySQLi, 5.7) / tests	2m 49s
DatabaseLive (8.1, OCI8, 8.0) / tests	5m 56s
DatabaseLive (8.1, MySQLi, 8.0) / tests	5m 1s
DatabaseLive (8.1, Postgre, 8.0) / tests	2m 30s
DatabaseLive (8.1, SQLite3, 8.0) / tests	2m 44s
DatabaseLive (8.1, SQLSRV, 8.0) / tests	4m 40s
DatabaseLive (8.2, MySQLi, 8.0) / tests	5m 8s
DatabaseLive (8.2, OCI8, 8.0) / tests	6m 42s
DatabaseLive (8.2, Postgre, 8.0) / tests	3m 16s
DatabaseLive (8.2, SQLite3, 8.0) / tests	3m 14s
DatabaseLive (8.2, SQLSRV, 8.0) / tests	5m 24s
DatabaseLive (8.3, MySQLi, 8.0) / tests	4m 31s
DatabaseLive (8.3, OCI8, 8.0) / tests	6m 18s
DatabaseLive (8.3, Postgre, 8.0) / tests	2m 48s
DatabaseLive (8.3, SQLite3, 8.0) / tests	3m 23s
DatabaseLive (8.3, SQLSRV, 8.0) / tests	4m 16s
SeparateProcess (8.1) / tests	3m 26s
SeparateProcess (8.2) / tests	3m 53s
CacheLive (8.2) / Cache Live Tests	2m 26s
CacheLive (8.1) / Cache Live Tests	2m 8s
CacheLive (8.3) / Cache Live Tests	2m 0s
SeparateProcess (8.3) / tests	3m 53s
Upload coverage results to Coveralls / coveralls	42s
	1h 36m 2s

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