show_ident_date: fix tz range check

Commit 1dca155f (log: handle integer overflow in
timestamps, 2014-02-24) tried to catch integer overflow
coming from strtol() on the timezone field by comparing against
LONG_MIN/LONG_MAX. However, the intermediate "tz" variable
is an "int", which means it can never be LONG_MAX on LP64
systems; we would truncate the output from strtol before the
comparison.

Clang's -Wtautological-constant-out-of-range-compare notices
this and rightly complains.

Let's instead store the result of strtol in a long, and then
compare it against INT_MIN/INT_MAX. This will catch overflow
from strtol, and also overflow when we pass the result as an
int to show_date.
Reported-by: NEric Sunshine <sunshine@sunshineco.com>
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

pretty.c

@@ -397,7 +397,7 @@ static const char *show_ident_date(const struct ident_split *ident,
 				   enum date_mode mode)
 {
 	unsigned long date = 0;
-	int tz = 0;
+	long tz = 0;
 
 	if (ident->date_begin && ident->date_end)
 		date = strtoul(ident->date_begin, NULL, 10);
@@ -406,7 +406,7 @@ static const char *show_ident_date(const struct ident_split *ident,
 	else {
 		if (ident->tz_begin && ident->tz_end)
 			tz = strtol(ident->tz_begin, NULL, 10);
-		if (tz == LONG_MAX || tz == LONG_MIN)
+		if (tz >= INT_MAX || tz <= INT_MIN)
 			tz = 0;
 	}
 	return show_date(date, tz, mode);