read-cache: fix leaking hash context in do_write_index()

When writing an index with the EOIE extension we allocate a separate
hash context. We never free that context though, causing a memory leak.
Plug it.

This leak is exposed by t9210, but plugging it alone does not make the
whole test suite pass.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

read-cache.c

@@ -3124,6 +3124,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	if (f)
 		free_hashfile(f);
 	strbuf_release(&sb);
+	free(eoie_c);
 	free(ieot);
 	return ret;
 }