Pipeline fails if only CONCOCT is turned on and other binners off

[jfy133]

Description of the bug

Fails due to the if/else statement around input to SPLIT_FASTA in binning.nf only consideres maxbin2 and/or metabat or both (CONCOCT does not produce 'unbins'). Should add logic to account for this, and allow pipeline to continue even after without SPLIT_FASTA

Command used and terminal output

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Relevant files

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System information

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