Put diff without whitespace option on every page with a diff

Disclaimer: currently this feature is not working anyway, see https://github.com/sindresorhus/refined-github/issues/322

Ideally the diff without whitespace button should be on every page with a diff having the diff options.

Until now the Files changed tab of a PR and compare pages wer not included for that feature even though they support the `?w=0` param.

extension/content.js

@@ -393,7 +393,7 @@ document.addEventListener('DOMContentLoaded', () => {
 				showRealNames();
 			}
 
-			if (pageDetect.isCommit() || pageDetect.isSingleCommit()) {
+			if (pageDetect.hasDiff()) {
 				addDiffViewWithoutWhitespaceOption('commit');
 			}