Return error in the error branch

This change fixes the issue when there is an error in decoding, where
the original code would return no error and false for ok. That would
confuse the calling function.

decode.go

@@ -184,7 +184,7 @@ func (d *Decoder) readLine(v reflect.Value) (err error, ok bool) {
 
 	rawValue, err := newRawValue(line, d.useCodepointIndices)
 	if err != nil {
-		return
+		return err, false
 	}
 	t := v.Type()
 	if t == d.lastType {