convert trivial cases to ALLOC_ARRAY

Each of these cases can be converted to use ALLOC_ARRAY or
REALLOC_ARRAY, which has two advantages:

  1. It automatically checks the array-size multiplication
     for overflow.

  2. It always uses sizeof(*array) for the element-size,
     so that it can never go out of sync with the declared
     type of the array.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

show-index.c

@@ -50,7 +50,8 @@ int main(int argc, char **argv)
 			unsigned char sha1[20];
 			uint32_t crc;
 			uint32_t off;
-		} *entries = xmalloc(nr * sizeof(entries[0]));
+		} *entries;
+		ALLOC_ARRAY(entries, nr);
 		for (i = 0; i < nr; i++)
 			if (fread(entries[i].sha1, 20, 1, stdin) != 1)
 				die("unable to read sha1 %u/%u", i, nr);