OZG-1614 fix contentType

goofy-client/libs/ozg-file/src/lib/ozg-file-container/ozg-file/ozg-file.component.ts

@@ -37,7 +37,7 @@ export class OzgFileComponent {
 	}
 
 	dragStart(event) {
-		if (!!this.file.contentType || this.file.contentType === '')  this.file.contentType = undefined;
+		if (!!this.file.contentType || this.file.contentType === '')  this.file.contentType = 'application/octet-stream';
 		const downloadUrl = `${ this.file.contentType }:${ this.file.name }:${ getUrl(this.file, OzgFileLinkRel.DOWNLOAD)}`
 		console.log(downloadUrl);
 		event.dataTransfer.setData("DownloadURL", downloadUrl);