Fix potential problem with multiple content iframes

program/js/app.js

@@ -10681,19 +10681,19 @@ function rcube_webmail() {
 
     this.resize_preview_iframe = function (iframe) {
         // Cancel runs that we're scheduled ealier but didn't run yet.
-        if (this.resizePreviewIframeTimer) {
-            clearTimeout(this.resizePreviewIframeTimer);
+        if (iframe.resizePreviewIframeTimer) {
+            clearTimeout(iframe.resizePreviewIframeTimer);
         }
         // Using setTimeout to put this at the end of the call stack.
-        this.resizePreviewIframeTimer = setTimeout(() => {
+        iframe.resizePreviewIframeTimer = setTimeout(() => {
             // Reset the height to avoid growing it bigger and bigger (due to
             // our adding of 20 pixels, and 8 extra pixels of unknown origin,
             // which are always added.
             iframe.style.height = '';
             var wantedHeight = iframe.contentDocument.firstChild.scrollHeight;
             // Add a few pixels to avoid problems with wrapped lines.
             iframe.style.height = wantedHeight + 20 + 'px';
-            this.resizePreviewIframeTimer = null;
+            iframe.resizePreviewIframeTimer = null;
         }, 50);
     };
 } // end object rcube_webmail