Handle slow loading of images

Internet Explorer seems to flag images as loaded prematurely, which
can result in rendering bugs. We can detect this by looking at the
dimensions though.

kasmweb/core/display.js

@@ -360,8 +360,14 @@ export default class Display {
     }
 
     imageRect(x, y, w, h, mime, arr) {
+        /* The internal logic cannot handle empty images, so bail early */
+        if ((width === 0) || (height === 0)) {
+            return;
+        }
+
         const img = new Image();
         img.src = "data: " + mime + ";base64," + Base64.encode(arr);
+
         this._renderQ_push({
             'type': 'img',
             'img': img,
@@ -621,7 +627,8 @@ export default class Display {
                     this.blitRgbxImage(a.x, a.y, a.width, a.height, a.data, 0, true);
                     break;
                 case 'img':
-                    if (a.img.complete) {
+                    /* IE tends to set "complete" prematurely, so check dimensions */
+                    if (a.img.complete && (a.img.width !== 0) && (a.img.height !== 0)) {
                         this.drawImage(a.img, a.x, a.y, a.w, a.h);
                     } else {
                         a.img._noVNC_display = this;