Fix for loading SVG in Safari. (#212)

* Fix for loading SVG in Safari.

* Tidier code

src/lib/missing-types.d.ts

@@ -1,5 +1,5 @@
 interface HTMLImageElement {
-  decode: () => Promise<void> | undefined;
+  decode: (() => Promise<void>) | undefined;
 }
 
 interface CanvasRenderingContext2D {

src/lib/util.ts

@@ -90,18 +90,20 @@ export async function blobToImg(blob: Blob): Promise<HTMLImageElement> {
     const img = new Image();
     img.decoding = 'async';
     img.src = url;
+    const loaded = new Promise((resolve, reject) => {
+      img.onload = () => resolve();
+      img.onerror = () => reject(Error('Image loading error'));
+    });
 
     if (img.decode) {
-      // Nice off-thread way supported in at least Safari.
+      // Nice off-thread way supported in Safari/Chrome.
-      await img.decode();
+      // Safari throws on decode if the source is SVG.
-    } else {
+      // https://bugs.webkit.org/show_bug.cgi?id=188347
-      // Main thread decoding :(
+      await img.decode().catch(() => null);
-      await new Promise((resolve, reject) => {
-        img.onload = () => resolve();
-        img.onerror = () => reject(Error('Image loading error'));
-      });
     }
 
+    // Always await loaded, as we may have bailed due to the Safari bug above.
+    await loaded;
     return img;
   } finally {
     URL.revokeObjectURL(url);