Minor Bugfix: ftype key in remote_dict and local_dict static through iteration

The ftype key in the `remote_dict` and `local_dict` was remaining static even though the code was iterating through the `arr` list (e.g. `arr = ['fitex','fitacf','lmfit']`). The consequence was that if no `fitex` files were found then `radDataOpen` or `sdDataOpen` would appear to be looking for `fitacf` and `lmfit` files next, but `ftype` in `remote_dict` or `local_dict` would still be set to `fitex`.

To see for yourself, you will need to add a print statement in `radDataOpen` or `sdDataOpen` after line 312 (https://github.com/vtsuperdarn/davitpy/blob/develop/pydarn/sdio/radDataTypes.py#L312) or after line 261 (https://github.com/vtsuperdarn/davitpy/blob/develop/pydarn/sdio/sdDataTypes.py#L261). Look for a file that can't yet exist, for example, something from the future.

This is a very simple and minor bugfix.