Browser compat fix.

Author: topboy

src/FormDataEncoder.ts

@@ -201,11 +201,12 @@ export class FormDataEncoder {
     const size = isFile(value) ? value.size : value.byteLength
     if (
       this.#options.enableAdditionalHeaders === true
-        && size != null
-        && !isNaN(size)
+      && size != null
+      && !isNaN(size)
     ) {
       header += `${this.#CRLF}Content-Length: ${
-        isFile(value) ? value.size : value.byteLength
+        isFile(value)
+          ? value.size : value.byteLength
       }`
     }
 
@@ -336,7 +337,15 @@ export class FormDataEncoder {
   async* encode(): AsyncGenerator<Uint8Array, void, undefined> {
     for (const part of this.values()) {
       if (isFile(part)) {
-        yield* part.stream()
+        const stream: any = part.stream()
+        if (stream.getReader instanceof Function) {
+          const reader: any = stream.getReader()
+          let result
+          do {
+            result = await reader.read()
+            if (result.value) yield result.value
+          } while (!result.done)
+        } else yield* stream
       } else {
         yield part
       }