remove redundant checking

Author: Erki Märks

constraints.go

@@ -257,7 +257,7 @@ func parseConstraint(c string) (*constraint, error) {
 		minorDirty := false
 		dirty := false
 
-		if (isX(m[3]) || m[3] == "") && len(m) > 8 && m[7] != "" && isX(strings.TrimPrefix(m[8], ".")) {
+		if isX(m[3]) && len(m) > 8 && m[7] != "" && isX(strings.TrimPrefix(m[8], ".")) {
 			ver = fmt.Sprintf("0.0.0-%s.0", strings.Split(m[7], ".")[0])
 			dirty = true
 			prereleaseDirty = true