fmt: Scan(&int) was mishandling a lone zero.

It took it as an octal base prefix but assumed more digits were coming.
Fixes #2077.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/4764044

src/pkg/fmt/scan.go

@@ -550,10 +550,12 @@ func (s *ss) getBase(verb int) (base int, digits string) {
 
 // scanNumber returns the numerical string with specified digits starting here.
 func (s *ss) scanNumber(digits string, haveDigits bool) string {
+	if !haveDigits {
 		s.notEOF()
-	if !haveDigits && !s.accept(digits) {
+		if !s.accept(digits) {
 			s.errorString("expected integer")
 		}
+	}
 	for s.accept(digits) {
 	}
 	return s.buf.String()

src/pkg/fmt/scan_test.go

@@ -298,6 +298,8 @@ var scanfTests = []ScanfTest{
 	// Fixed bugs
 	{"%d\n", "27\n", &intVal, 27},  // ok
 	{"%d\n", "28 \n", &intVal, 28}, // was: "unexpected newline"
+	{"%v", "0", &intVal, 0},        // was: "EOF"; 0 was taken as base prefix and not counted.
+	{"%v", "0", &uintVal, uint(0)}, // was: "EOF"; 0 was taken as base prefix and not counted.
 }
 
 var overflowTests = []ScanTest{