Support custom chunks which might have no parent.

Some other plugins might create custom chunks which might have no parent.(getParents returns empty array)

Author: TotooriaHyperion

src/lib/does-chunk-belong-to-html.js

@@ -47,6 +47,7 @@ function recursiveChunkEntryName (chunk) {
 }
 
 function _recursiveChunkGroup (chunkGroup) {
+  if (!chunkGroup) return undefined;
   if (chunkGroup instanceof EntryPoint) {
     return chunkGroup.name
   } else {