Fix for issue 9518 (#9520)

* Add regression test for #9518

* 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

@@ -0,0 +1,27 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "width": 8,
+      "height": 8
+    }
+  },
+  "zoom": 3,
+  "sources": {},
+  "sprite": "local://sprites/emerald",
+  "layers": [
+    {
+      "id": "background",
+      "type": "background",
+      "paint": {
+        "background-pattern": [
+          "step",
+          ["zoom"],
+          "",
+          5,
+          "cemetery_icon"
+        ]
+      }
+    }
+  ]
+}