Check needed for trace data not present in unzipped traces

Could be good to add a check or logging to show if/when a trace doesn't exist in the unzipped file directory (`input_directory` in parse_{wind/solar}_traces functions) when parsing traces. 
E.g., Rez N12 has no VRE traces in the download from AEMO but currently no warning/logging shows up when parsing area traces to highlight that it doesn't exist at this step.