Blender Git Loki

LibOverride: Better handling of missing linked data during resync.

We do not generate overrides for missing data-blocks (aka placeholder
ones) anymore, and properly delete the remaining old overrides of those
during the resync process.

This should prevent constant 'missing data-blocks' messages when opening
blend files with overrides whose libraries have beed edited.

Issue reported by @andy from Blender studio, thanks.