Fix IndexError: strip() before checking for empty value

[jvanmalder]

I encountered the following error when trying to execute a bulk insert:

File "/usr/local/bin/redisgraph-bulk-loader", line 8, in <module>
    sys.exit(bulk_insert())
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.9/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/redisgraph_bulk_loader/bulk_insert.py", line 118, in bulk_insert
    process_entities(labels)
  File "/usr/local/lib/python3.9/site-packages/redisgraph_bulk_loader/bulk_insert.py", line 31, in process_entities
    entity.process_entities()
  File "/usr/local/lib/python3.9/site-packages/redisgraph_bulk_loader/label.py", line 66, in process_entities
    row_binary = self.pack_props(row)
  File "/usr/local/lib/python3.9/site-packages/redisgraph_bulk_loader/entity_file.py", line 275, in pack_props
    props.append(inferred_prop_to_binary(field))
  File "/usr/local/lib/python3.9/site-packages/redisgraph_bulk_loader/entity_file.py", line 148, in inferred_prop_to_binary
    if prop_val[0] == '[' and prop_val[-1] == ']':
IndexError: string index out of range

This happened because:

1. Empty strings are handled first (see here)
2. Then the property value is stripped (see here)
3. Then the property value is accessed as if it wasn't empty (see here)

So in the case where the property value is just a bunch of space tokens, all of those are stripped away in step 2, firing off the IndexError in step 3.

It's quite a simple fix, by just stripping first before checking for the empty string.

[jeffreylovitz]

Good catch, @jvanmalder! Thank you for the PR.