fix(api): update message handling to check for undefined response (#129)

Author: dadamu

api/browser.ts

@@ -186,7 +186,7 @@ export class KastleBrowserAPI {
       const onMessage = async (event: MessageEvent<unknown>) => {
         try {
           const result = callback(event);
-          if (!result) {
+          if (result === undefined) {
             return; // Skip if the result is empty, which means the message is not for this channel
           }
 

api/ethereum.ts

@@ -126,7 +126,7 @@ export class EthereumBrowserAPI {
       const onMessage = async (event: MessageEvent<unknown>) => {
         try {
           const result = callback(event);
-          if (!result) {
+          if (result === undefined) {
             return; // Skip if the result is empty, which means the message is not for this channel
           }