fixed issue #265

Former-commit-id: 015a6281ca4870ec70aa4d5b1bdef6e0b4838de2

lib/single-file/single-file-util.js

@@ -235,7 +235,7 @@ this.singlefile.lib.util = this.singlefile.lib.util || (() => {
 							return { data: "data:base64,", resourceURL };
 						} else {
 							const reader = new FileReader();
-							reader.readAsDataURL(new Blob([buffer], { type: contentType || this.getContentType() }));
+							reader.readAsDataURL(new Blob([buffer], { type: contentType }));
 							const dataUri = await new Promise((resolve, reject) => {
 								reader.addEventListener("load", () => resolve(reader.result), false);
 								reader.addEventListener("error", reject, false);