Make preprocess_single work even if files are missing

[2320sharon]

If a file is missing in preprocess_single return None and just skip this file.

Tasks

• Check if each file needed to run preprocess_single exists or not
• If its missing return None
• Maybe log why it failed - '{FILENAME} was missing from {EXPECTED_LOCATION}'

Relevant Code

# fn is a list of 3 file names typically is ['ms_filename','mask_filename','pan/swir filename']
# the snippet below is from the landsat 5 code section
        fn_ms = fn[0]
        fn_mask = fn[1]
       # HERE IS WHERE IT SHOULD BE CHECKED IF ALL FILES IN FN EXIST OR NOT
        # read ms bands
        data = gdal.Open(fn_ms, gdal.GA_ReadOnly)
        # if  fn_ms doesn't exist this code will return None
        georef = np.array(data.GetGeoTransform())

Exceptions Caused by this issue

File ~\anaconda3\envs\coastseg_transformers10\lib\site-packages\coastsat\SDS_shoreline.py:249, in extract_shorelines(metadata, settings)
    239 shoreline_date = os.path.basename(fn[0])[:19]
    241 # preprocess image (cloud mask + pansharpening/downsampling)
    242 (
    243     im_ms,
    244     georef,
    245     cloud_mask,
    246     im_extra,
    247     im_QA,
    248     im_nodata,
--> 249 ) = SDS_preprocess.preprocess_single(
    250     fn,
    251     satname,
    252     settings["cloud_mask_issue"],
    253     settings["pan_off"],
    254     collection,
    255     apply_cloud_mask,
    256 )
    257 # get image spatial reference system (epsg code) from metadata dict
    258 image_epsg = metadata[satname]["epsg"][i]

File ~\anaconda3\envs\coastseg_transformers10\lib\site-packages\coastsat\SDS_preprocess.py:462, in preprocess_single(fn, satname, cloud_mask_issue, pan_off, collection, do_cloud_mask)
    460 # read ms bands
    461 data = gdal.Open(fn_ms, gdal.GA_ReadOnly)
--> 462 georef = np.array(data.GetGeoTransform())
    463 bands = read_bands(fn_ms)
    464 im_ms = np.stack(bands, 2)

AttributeError: 'NoneType' object has no attribute 'GetGeoTransform'