More thorough input checks for isPatternMissing function

Fixes regression introduced by #9380

ResolvedImage.fromString may now return null, which potentially leaves CrossFaded<ResolvedImage>
with missing image patterns

I have traced other code paths using ResolvedImage.fromString and have not seen
any other potential offenders

src/render/painter.js

@@ -589,6 +589,7 @@ class Painter {
      */
     isPatternMissing(image: ?CrossFaded<ResolvedImage>): boolean {
         if (!image) return false;
+        if (!image.from || !image.to) return true;
         const imagePosA = this.imageManager.getPattern(image.from.toString());
         const imagePosB = this.imageManager.getPattern(image.to.toString());
         return !imagePosA || !imagePosB;

test/integration/render-tests/regressions/mapbox-gl-js#9518/style.json

@@ -2,8 +2,8 @@
   "version": 8,
   "metadata": {
     "test": {
-      "width": 64,
-      "height": 64
+      "width": 8,
+      "height": 8
     }
   },
   "zoom": 3,