check for the pattern maps files existence #27
Description
In line https://github.com/parsotat/BatAnalysis/blob/211c802990a80058d3036c4a7c34c9d8e1817a81/batanalysis/bat_survey.py#L254C43-L254C57 it is possible for the directory to exist but the files to not be there. This should produce an error.