Address minor bug when appending records

[jhmigueles]

Fixes #1162 => When appending records with maxRecordingInterval, if any of the recording files does not have enough data (part 1 M$metashort == NULL), then it used to trigger an error because it also tries to append this recording.

Checklist before merging:

• Existing tests still work (check by running the test suite, e.g. from RStudio).
• Added tests (if you added functionality) or fixed existing test (if you fixed a bug).
• Clean code has been attempted, e.g. intuitive object names and no code redundancy.
• Documentation updated:
  • Function documentation
  • Chapter vignettes for GitHub IO
  • Vignettes for CRAN
• Corresponding issue tagged in PR message. If no issue exist, please create an issue and tag it.
• Updated release notes in inst/NEWS.Rd with a user-readable summary. Please, include references to relevant issues or PR discussions.
• Added your name to the contributors lists in the DESCRIPTION file, if you think you made a significant contribution.
• GGIR parameters were added/removed. If yes, please also complete checklist below.

If NEW GGIR parameter(s) were added then these NEW parameter(s) are:

• documented in man/GGIR.Rd
• included with a default in R/load_params.R
• included with value class check in R/check_params.R
• included in table of vignettes/GGIRParameters.Rmd with references to the GGIR parts the parameter is used in.
• mentioned in NEWS.Rd as NEW parameter

If GGIR parameter(s) were deprecated these parameter(s) are:

• documented as deprecated in man/GGIR.Rd
• removed from R/load_params.R
• removed from R/check_params.R
• removed from table in vignettes/GGIRParameters.Rmd
• mentioned as deprecated parameter in NEWS.Rd
• added to the list in R/extract_params.R with deprecated parameters such that these do not produce warnings when found in old config.csv files.

[vincentvanhees]

Thanks, could you rephrase in NEWS.md "Part 1: Fix minor bug when appending records if any of the files has not enough data to produce meaningful metashort and metalong objects in part 1." to "Part 1: When appending records ignore files that have not enough data to produce meaningful metashort and metalong objects in part 1."

Motivation:

• This is not a bug because the code was never designed to handle this scenario. I wrote the code to append real recordings. Please try to avoid the word "bug" if it is not a mistake in coding as that sounds like we are making mistakes all the time.
• This does not allow for appending empty files, it ignores the empty file, which is not the same.