BUG: NodeTypeManager can crash in cli context

[mhsdesign]

I found out that flow nodetypes:list can throw an error

No base URI could be provided.
This probably means a call was made outside of an HTTP request and a base
URI was neither configured nor specified as $fallbackRequest.

  Type: Neos\Flow\Http\Exception
  Code: 1567529953
  File: Data/Temporary/Development/Cache/Code/Flow_Object_Classes/Neos_Flow_Http_Ba
        seUriProvider.php
  Line: 9

that was caused by me using the thumbnail option which is post processed here (introduced with 277989f)

neos-development-collection/Neos.Neos/Classes/Aspects/NodeTypeConfigurationEnrichmentAspect.php

Line 144 in 6b338b4

$thumbnailUrl = $this->resourceManager->getPublicPackageResourceUriByPath($thumbnailUrl);

of course this logic already seems a bit hacky and we could move this out to the neos ui to use an endpoint for resolving the uri neos/neos-ui#3695, but still that code alone should not crash on cli.

i would propose that just / is used as base uri if nothing is found.

flow nodetypes:show Neos.Demo:Document.Page --path ui.help.thumbnail
NodeType configuration "Neos.Demo:Document.Page.ui.help.thumbnail":

/_Resources/Static/Packages/Neos.Neos/Images/dummy-image.svg