cleanup: Make group packet entry creation less error-prone

[JFreegman]

We always assumed that create_array_entry() would only be called with an empty array entry and wouldn't modify entries on error. We now explicitly require both conditions, and also give an error in the case of a non-null data pointer with a zero length field, as this indicates a logic error.

Checks for an empty array entry that precede a call to create_array_entry() are now redundant. It should be noted that a non-empty entry doesn't necessarily indicate an error. This condition can be triggered if packets are being sent or received faster than they can be processed/acknowledged, which is common when spamming messages on poor connections.

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This change is 

[JFreegman]

This cleanup found a bug, which is fixed in #2541

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (5b9c420) 69.08% compared to head (6b6718e) 69.02%.

Files	Patch %	Lines
toxcore/group_connection.c	50.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2540      +/-   ##
==========================================
- Coverage   69.08%   69.02%   -0.07%     
==========================================
  Files          96       96              
  Lines       28052    28049       -3     
==========================================
- Hits        19381    19362      -19     
- Misses       8671     8687      +16     

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[nurupo]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @iphydf and @JFreegman)

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-- commits line 15 at r2:
What width do you use for the commit message body? Seems to be shorter than the typical 72 columns. Looks like 64 or 65?

[JFreegman]

-- commits line 15 at r2:

Previously, nurupo wrote…

What width do you use for the commit message body? Seems to be shorter than the typical 72 columns. Looks like 64 or 65?

I just eyeball it. Is there a way to force commit messages to print a newline at a specific column via terminal?

[nurupo]

-- commits line 15 at r2:

Previously, JFreegman wrote…

I just eyeball it. Is there a way to force commit messages to print a newline at a specific column via terminal?

You could check the line wrapping functionality of your terminal text editor.

If you are using nano, you can add set fill 0 into your .nanorc file, which will make it wrap using the screen width, so if you resize your terminal window to be 72 characters long (some terminal emulators show you the new size while you resize the window so it's very easy to tell) and then press Ctrl+j while having a cursor in a paragraph to wrap (justify) just that paragraph, or Alt+j to wrap the entire buffer -- that would wrap the text at 72 characters on whitespace, Of course you could just do set fill 72 and then it would wrap to 72 no matter the terminal window size, but I like the flexibility of 0.

You can also get your commit message spellchecked by adding set speller "aspell -x -c" to .nanorc and pressing F12 to spellcheck. (I'm actually having nano invoke a wrapper bash script instead of invoking aspell directly, which keeps a personal dictionary file per git repository where aspell adds per-project words, to avoid aspell triggering on a ton of technical jargon used in a git repository that is not part of the English dictionary.)

[Green-Sky]

Reviewed 1 of 2 files at r3, 1 of 1 files at r4, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @JFreegman)