revision: parse "git log -<count>" more carefully

This mistyped command line simply ignores "master" and ends up
showing two commits from the current HEAD:

    $ git log -2master

because we feed "2master" to atoi() without making sure that the
whole string is parsed as an integer.

Use the strtol_i() helper function instead.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

revision.c

@@ -1613,7 +1613,9 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		return argcount;
 	} else if ((*arg == '-') && isdigit(arg[1])) {
 		/* accept -<digit>, like traditional "head" */
-		revs->max_count = atoi(arg + 1);
+		if (strtol_i(arg + 1, 10, &revs->max_count) < 0 ||
+		    revs->max_count < 0)
+			die("'%s': not a non-negative integer", arg + 1);
 		revs->no_walk = 0;
 	} else if (!strcmp(arg, "-n")) {
 		if (argc <= 1)