Validate and trim spaces on WM pointer

Ref T773

database.go

@@ -907,12 +907,26 @@ func (db *datastore) UpdateCollection(c *SubmittedCollection, alias string) erro
 
 	// Update Monetization value
 	if c.Monetization != nil {
+		skipUpdate := false
+		if *c.Monetization != "" {
+			// Strip away any excess spaces
+			trimmed := strings.TrimSpace(*c.Monetization)
+			// Only update value when it starts with "$", per spec: https://paymentpointers.org
+			if strings.HasPrefix(trimmed, "$") {
+				c.Monetization = &trimmed
+			} else {
+				// Value appears invalid, so don't update
+				skipUpdate = true
+			}
+		}
+		if !skipUpdate {
 			_, err = db.Exec("INSERT INTO collectionattributes (collection_id, attribute, value) VALUES (?, ?, ?) ON DUPLICATE KEY UPDATE value = ?", collID, "monetization_pointer", *c.Monetization, *c.Monetization)
 			if err != nil {
 				log.Error("Unable to insert monetization_pointer value: %v", err)
 				return err
 			}
 		}
+	}
 
 	// Update rest of the collection data
 	res, err = db.Exec("UPDATE collections SET "+q.Updates+" WHERE "+q.Conditions, q.Params...)