Break build when resource is invalid and ignoreMissingResources = false

Somehow the incrementalBuilding-Feature broke the behaviour that ignoreMissingResource should provide.
This PR throws a MojoExecutionException if a resource is invalid and ignoreMissingResource is set to false.
I would rather let the build pass and assume the resource changed, instead of failing it because I couldn't identify if there is a change or not. Do you have good argument for doing the other way around?