FIX: skip empty lines in read_raw_eyelink

[scott-huberty]

This PR Fixes a problem with reading an Eyelink file that was raised on the Discussion forum: https://mne.discourse.group/t/issue-with-read-raw-eyelink/7787

The problematic file provided by the researcher had a line that only contained a newline character, which broke the parser.
This branch checks for and skips empty lines, fixing the problem.

I did a quick performance check to see how much longer file reading takes with the additional checks:

import mne
fname = mne.datasets.eyelink.data_path() / "eeg-et" / "sub-01_task-plr_eyetrack.asc"
%timeit mne.io.read_raw_eyelink(fname)

on main:

860 ms ± 30.4 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

on this branch:

997 ms ± 139 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

[mscheltienne]

Thanks @scott-huberty!