Performance: Skip modules with no files from search patterns

[ewels]

MultiQC execution runs in a few distinct steps. First, the file-search mechanism finds files based on the search pattern identifiers, then the modules are run.

Currently, I am pretty sure that all modules always run. We could potentially get a small performance improvement by entirely skipping a module if the search pattern returned no files. Each module should be doing very little in this case, so it might not have much effect, but could be an easy thing to implement.