fixup! Hydrate missing loose objects in check_and_freshen()

If the `read-object` hook is not found, the code currently would fail
with the rather obscure message:

	fatal: Out of memory, strdup failed

The reason is because without a check whether the hook was found,
eventually `strvec_push()` would try to call `xstrdup()` with `cmd`
(which is `NULL` if the hook was not found) which would fail and print
that rather misleading message.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

odb.c

@@ -725,6 +725,9 @@ int read_object_process(struct repository *r, const struct object_id *oid)
 	const char *cmd = find_hook(r, "read-object");
 	uint64_t start;
 
+	if (!cmd)
+		die(_("could not find the `read-object` hook"));
+
 	start = getnanotime();
 
 	trace2_region_enter("subprocess", "read_object",r);