Fix bug with grpc decompression in body formatting

The headers field is optional, and we didn't actually provide it in this
case, and grpc decompression would fail without that metadata.

Author: pimterry

src/components/editor/content-viewer.tsx

@@ -143,7 +143,7 @@ export class ContentViewer extends React.Component<ContentViewerProps> {
         const cachedValue = cache.get(cacheKey) as ObservablePromise<string> | string | undefined;
 
         const renderingContent = cachedValue ||
-            this.formatter.render(this.contentBuffer) as ObservablePromise<string> | string;
+            this.formatter.render(this.contentBuffer, this.props.headers) as ObservablePromise<string> | string;
         if (!cachedValue) cache.set(cacheKey, renderingContent);
 
         if (typeof renderingContent === 'string') {