[Fix] ECG delineator peak index

[danibene]

Description

This PR aims to fix an error in ecg_delineate() where invalid indices were returned. See also #729

Proposed Changes

I changed the ecg_delineate() function so that within _ecg_delineator_peak(), all indices of fiducial points are checked to ensure that they are not larger than the number of samples in the ECG signal - 1

Checklist

Here are some things to check before creating the PR. If you encounter any issues, do let us know :)

• I have read the CONTRIBUTING file.
• My PR is targeted at the dev branch (and not towards the master branch).
• I ran the CODE CHECKS on the files I added or modified and fixed the errors. (I only actively corrected sections of the code that I modified here)

[codeclimate]

Code Climate has analyzed commit 8331d3c and detected 0 issues on this pull request.

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[danibene]

Also should we add https://github.com/neuropsychology/NeuroKit/files/9758396/debug.csv to https://github.com/neuropsychology/NeuroKit/tree/master/tests/ecg_data & use the code that led to the error as a test for ecg_delineate()? I just tested it by installing my branch:

Pip install: https://gist.github.com/danibene/8b5df2192b5a063d10e59972d77556d6
Installing my branch: https://gist.github.com/danibene/6cb93f7c2654698b91f0f3a5de2e8166

but maybe it'd be good to have it as a proper test?

[codecov-commenter]

Codecov Report

Base: 53.33% // Head: 53.32% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (8331d3c) compared to base (c88602e).
Patch coverage: 93.47% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #731      +/-   ##
==========================================
- Coverage   53.33%   53.32%   -0.01%     
==========================================
  Files         283      283              
  Lines       12844    12845       +1     
==========================================
  Hits         6850     6850              
- Misses       5994     5995       +1     

Impacted Files	Coverage Δ
neurokit2/ecg/ecg_delineate.py	79.36% <93.33%> (-0.12%)	⬇️
neurokit2/signal/signal_formatpeaks.py	81.25% <100.00%> (ø)
neurokit2/signal/signal_fixpeaks.py	72.90% <0.00%> (-0.11%)	⬇️

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[DominiqueMakowski]

Ah nice, thanks for digging into the delineator code, it's a tough one :)