time: make Parse validate day's lower bound in addition to upper bound

Day 0 is as invalid as day 32.

Fixes #17874

Change-Id: I52109d12bafd6d957d00c44d540cb88389fff0a7
Reviewed-on: https://go-review.googlesource.com/33429
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/time/format.go

@@ -1012,7 +1012,7 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 	}
 
 	// Validate the day of the month.
-	if day > daysIn(Month(month), year) {
+	if day < 1 || day > daysIn(Month(month), year) {
 		return Time{}, &ParseError{alayout, avalue, "", value, ": day out of range"}
 	}
 

src/time/format_test.go

@@ -224,6 +224,7 @@ var dayOutOfRangeTests = []struct {
 	{"Thu Nov 31 21:00:57 2010", false},
 	{"Thu Dec 31 21:00:57 2010", true},
 	{"Thu Dec 32 21:00:57 2010", false},
+	{"Thu Dec 00 21:00:57 2010", false},
 }
 
 func TestParseDayOutOfRange(t *testing.T) {