Encoder for GIF provides a Promise to getBuffer when a string, Buffer…

…, or Uint8Array is expected (#1239)

* Fixing Issue 980: The 'chunk' argument must be of type string or an instance of Buffer or Uint8Array. Received an instance of Promise.

* fix lint

---------

Co-authored-by: Andrew Lisowski <lisowski54@gmail.com>

packages/core/src/utils/image-bitmap.js

@@ -225,7 +225,15 @@ export function getBuffer(mime, cb) {
 
   if (this.constructor.encoders[mime]) {
     const buffer = this.constructor.encoders[mime](this);
-    cb.call(this, null, buffer);
+    // Typically, buffers return a string or map.  However, the gif library "gifwrap" seemingly returns promises.
+    if (buffer instanceof Promise) {
+      // trigger the callback when the promise has been resolved
+      buffer.then((buff) => {
+        cb.call(this, null, buff);
+      });
+    } else {
+      cb.call(this, null, buffer);
+    }
   } else {
     return throwError.call(this, "Unsupported MIME type: " + mime, cb);
   }