fix: reset state before scanning (#189)

Fixes #185
Fixes #188

scan.go

@@ -31,6 +31,9 @@ func (z *Big) scan(r io.ByteScanner) error {
 	// We deviate a little by being a tad bit more forgiving. For instance,
 	// we allow case-insensitive nan and infinity values.
 
+	// Before scanning, reset it to zero
+	z.SetUint64(0)
+
 	// Sign
 	neg, err := scanSign(r)
 	if err != nil {

scan_test.go

@@ -51,3 +51,26 @@ func BenchmarkBig_SetString(b *testing.B) {
 	}
 	globOk = ok
 }
+
+
+
+func TestUnmarshalTextTwice(t *testing.T) {
+	x := &Big{}
+
+	x.UnmarshalText([]byte(`1`))
+	x.UnmarshalText([]byte(`2`))
+	if x.String() != "2" {
+		t.Errorf("wanted: %q, got %q", "2", x.String())
+	}
+}
+
+
+func TestSetStringTwice(t *testing.T) {
+	x := &Big{}
+
+	x.SetString("1")
+	x.SetString("2")
+	if x.String() != "2" {
+		t.Errorf("wanted: %q, got %q", "2", x.String())
+	}
+}