prevent failing on empty file

[pvgenuchten]

for none spatial or empty geojson file, ds seems None

Traceback (most recent call last):
  File "/opt/venv/bin/crawl-metadata", line 8, in <module>
    sys.exit(indexDir())
             ^^^^^^^^^^
  File "/opt/venv/lib/python3.12/site-packages/click/core.py", line 1485, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/venv/lib/python3.12/site-packages/click/core.py", line 1406, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/opt/venv/lib/python3.12/site-packages/click/core.py", line 1269, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/venv/lib/python3.12/site-packages/click/core.py", line 824, in invoke
    return callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/venv/lib/python3.12/site-packages/geodatacrawler/metadata.py", line 94, in indexDir
    processPath(dir, initialMetadata, mode, dbtype, dir_out, dir_out_mode, dir, resolve, prefix, profile)
  File "/opt/venv/lib/python3.12/site-packages/geodatacrawler/metadata.py", line 432, in processPath
    md = indexFile(fname)
         ^^^^^^^^^^^^^^^^
  File "/opt/venv/lib/python3.12/site-packages/geodatacrawler/utils.py", line 125, in indexFile
    for i in ds:
TypeError: 'NoneType' object is not iterable