Bugfix: Do not write manifest, when nothing changed

This leads to a loop of death, because every time the pipeline writes
the manifest again, the watcher picks it up. Then, the manifest file is
written again. Guess what? The watcher picks that up again...

Author: moonglum

lib/build-manifest-writer.js

@@ -12,8 +12,12 @@ module.exports = manifestConfig => {
 	let manifest = {};
 	return results => {
 		let filteredResults = results.filter(result => result.changed);
-		manifest = updateManifest(filteredResults, manifest, manifestConfig);
-		return writeManifest(filteredResults, manifest, manifestConfig);
+		if(filteredResults.length > 0) {
+			manifest = updateManifest(filteredResults, manifest, manifestConfig);
+			return writeManifest(filteredResults, manifest, manifestConfig);
+		} else {
+			return [];
+		}
 	};
 };