Fixed with tags behavior

- Made sure there are at least two arguments (because 0 % 2 == 0 so that check did not suffice)
- Set tagset capacity to correct size because that is exactly how long it must be when everything goes right
- Completely restructured for-loop to do what it was intended to do

Author: DerRidda

core/readpref/options.go

@@ -34,14 +34,15 @@ func WithMaxStaleness(ms time.Duration) Option {
 // overrides all previous calls to either method.
 func WithTags(tags ...string) Option {
 	return func(rp *ReadPref) error {
-		if len(tags)%2 != 0 {
+		l := len(tags)
+		if l < 2 || l % 2 != 0 {
 			return ErrInvalidTagSet
 		}
 
-		tagset := make(tag.Set, 0)
+		tagset := make(tag.Set, 0, l/2)
 
-		for i := 0; i < len(tags)/2; i++ {
-			tagset = append(tagset, tag.Tag{Name: tags[i], Value: tags[i+1]})
+		for i := 1; i < l; i+=2 {
+			tagset = append(tagset, tag.Tag{Name: tags[i-1], Value: tags[i]})
 		}
 
 		return WithTagSets(tagset)(rp)