dmrecon: remove "scale == -1" feature

Don't reconstruct L0-L4 when scale is -1.
dmrecon: improve error handling

* skip view if embedding is missing, don't crash
* show errors in FancyProgressPrinter
UMVE: fix two segfaults

* move view == NULL check in start_dmrecon_job
* fix crash when job is cancelled twice
Merge pull request #51 from Waldteufel/dmrecon-error-handling

dmrecon: error handling