add sound effect for NPC speech interaction

src/de/miaurizius/jgame2d/core/UI.java

@@ -301,6 +301,7 @@ public class UI {
             char[] characters = tradingNPC.dialogue[tradingNPC.dialogueSet][tradingNPC.dialogueIndex].toCharArray();
             if(charIndex < characters.length) {
                 String s = String.valueOf(characters[charIndex]);
+                panel.playSE(17);
                 combinedText = combinedText + s;
                 currentDialogue = combinedText;
                 charIndex++;