builtin/log: fix leak when showing converted blob contents

In `show_blob_object()`, we proactively call `textconv_object()`. In
case we have a textconv driver for this blob we will end up showing the
converted contents, otherwise we'll show the un-converted contents of it
instead.

When the object has been converted we never free the buffer containing
the converted contents. Fix this to plug this memory leak.

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

builtin/log.c

@@ -707,6 +707,7 @@ static int show_blob_object(const struct object_id *oid, struct rev_info *rev, c
 
 	write_or_die(1, buf, size);
 	object_context_release(&obj_context);
+	free(buf);
 	return 0;
 }