fixes#257

This PR contains a:

• bugfix
• newfeature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

As discussed in#257, when the plugin callsmodulesByChunkGroup, it calls the chunk group'sgetModuleIndex2() function from the ChunkGroup object's_moduleIndices2 Map property. However, the error occurs because the module it's trying to find the index for doesn't exist in_moduleIndices2, causingmodulesByChunkGroup to return an empty array. The for loop that uses the array never iterates, sobestMatch is never set and is left undefined, resulting in an error when trying to call.pop() on that undefined object.

This fix checks ifgetModuleIndex2() returns no matching modules and, if so, dives into each chunk in the chunk group to find matching modules.

Breaking Changes

None.

Additional Info

While this solution dives into a chunk group's chunks to find modules that weren't in the chunk group's_moduleIndices2 property, it might indicate a bug in webpack where that property is not being fully populated as it should be. If that is the case, then this fix should no longer be necessary, but perhaps it wouldn't hurt to have an extra guard for finding chunk modules.