optimize handling of 'incomplete' plot-files

[de-luxe]

create internal lookup with real number of nonces for plot-files, were size and specified size from filename does not match, to prevent checker from checking empty buffer.

[k06a]

I am mining while generating some files. Looks like miner uses unfinished files...

[Blagodarenko]

XPlotter blocks file for monopoly access while plotting

[k06a]

Right now I am creating plot files in subdirectory and move them to disk root after completion.

[de-luxe]

Yes, thats what i would suggest @k06a , miner will also (try to) mine unfinished plotfiles, if they are within the specified plotFilePaths ... depending on plotter used this may lead to undefined behavior ...