help: fix leaking `struct cmdnames`

We're populating multiple `struct cmdnames`, but don't ever free them.
Plug this memory leak.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

help.c

@@ -723,6 +723,10 @@ const char *help_unknown_cmd(const char *cmd)
 				   (float)cfg.autocorrect/10.0, assumed);
 			sleep_millisec(cfg.autocorrect * 100);
 		}
+
+		cmdnames_release(&cfg.aliases);
+		cmdnames_release(&main_cmds);
+		cmdnames_release(&other_cmds);
 		return assumed;
 	}