fix(widget): call onReady against iframe (#7436)

Author: shoom3301

libs/widget-lib/src/cowSwapWidget.ts

@@ -69,10 +69,6 @@ export function createCowSwapWidget(container: HTMLElement, props: CowSwapWidget
   logWidget('Resolved trusted iframe origin', { iframeOrigin })
   const windowListeners: WindowListener[] = []
 
-  if (onReady) {
-    windowListeners.push(listenToReady(iframe.contentWindow || window, iframeOrigin, onReady))
-  }
-
   // 2. Clear the content (delete any previous iFrame if it exists)
   container.innerHTML = ''
   container.appendChild(iframe)
@@ -83,6 +79,10 @@ export function createCowSwapWidget(container: HTMLElement, props: CowSwapWidget
     throw new Error('Iframe does not contain a window!')
   }
 
+  if (onReady) {
+    windowListeners.push(listenToReady(iframeWindow, iframeOrigin, onReady))
+  }
+
   // 3. Send appCode (once the widget posts the ACTIVATE message)
   windowListeners.push(sendAppCodeOnActivation(iframeWindow, iframeOrigin, params.appCode))