fetch-pack: Avoid memcpy() with src==dst

memcpy() may only be used for disjoint memory areas, but when invoked
from cmd_fetch_pack(), we have my_args == &args.  (The argument cannot
be removed entirely because transport.c invokes with its own
variable.)

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fetch-pack.c

@@ -780,7 +780,8 @@ struct ref *fetch_pack(struct fetch_pack_args *my_args,
 	struct ref *ref_cpy;
 
 	fetch_pack_setup();
-	memcpy(&args, my_args, sizeof(args));
+	if (&args != my_args)
+		memcpy(&args, my_args, sizeof(args));
 	if (args.depth > 0) {
 		if (stat(git_path("shallow"), &st))
 			st.st_mtime = 0;