PrefixedFileProvider: Watch() may miss changes when glob contains '**'

[rameel]

PrefixedFileProvider.Watch() sometimes misses file change notifications.

Seems to happen when the glob filter contains **, especially if parts of the pattern overlap with the prefix structure.

var provider = new PrefixedFileProvider(
    "/modules/profile/assets",
    new PhysicalFileProvider(...));

var token = provider.Watch("/modules/**/assets/*.js");

In my case, changes to *.js files are not detected.