cleanup: fix possible overflow errors in binary search

A common mistake when writing binary search is to allow possible
integer overflow by using the simple average:

	mid = (min + max) / 2;

Instead, use the overflow-safe version:

	mid = min + (max - min) / 2;

This translation is safe since the operation occurs inside a loop
conditioned on "min < max". The included changes were found using
the following git grep:

	git grep '/ *2;' '*.c'

Making this cleanup will prevent future review friction when a new
binary search is contructed based on existing code.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -1277,7 +1277,7 @@ static int done_pbase_path_pos(unsigned hash)
 	int lo = 0;
 	int hi = done_pbase_paths_num;
 	while (lo < hi) {
-		int mi = (hi + lo) / 2;
+		int mi = lo + (hi - lo) / 2;
 		if (done_pbase_paths[mi] == hash)
 			return mi;
 		if (done_pbase_paths[mi] < hash)