Fix several tiny memory leaks

[Quipyowert2]

• What does this PR do?
  Fixes a series of very tiny leaks.

• Screenshots (if applicable)

• PR acceptance criteria (reminder only, please delete once read)

  • Your commit message(s) are descriptive. See:

    https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

  • [https://raw.githubusercontent.com/fvwmorg/fvwm3/master/doc/README]Documentation updated (where appropriate)

  • Style guide followed (try and match the surrounding code where possible)

  • All tests are passing: although this is automatic, Codacy will often
    highlight additional considerations which will need to be addressed before
    the PR can be merged.

• Issue number(s)

If this PR addresses any issues, please ensure the appropriate commit
message(s) contains:

Fixes #XXX

at the end of your commit message, where XXX should be replaced with the
relevant issue number.

If there is more than one issue fixed then use:

Fixes #XXX, fixes #YYY, fixes #ZZZ

[ThomasAdam]

Hi @Quipyowert2

Thanks, all look good. Not overly wild about the whole "Bool" checking in functions.c, but there's already a precendence for it.

See comments in-line for the FScreen.c change.

Can you also collapse these changes into one or two commits?

[Quipyowert2]

I added the error message you suggested and removed the must_free_name variable since it wasn't needed. I squashed the commits into one commit but the commit message is kind of long.

[ThomasAdam]

Thanks, @Quipyowert2

I would use a commit message of:

Assorted mem leak fixes

In running fvwm3 though valgrind, this commit fixes a few memory leaks it has detected.

[ThomasAdam]

Oops. Thanks for fixing this!

[Quipyowert2]

PeekToken moves action_cpy forward a few bytes so I had to introduce another variable to be able to free the original pointer. Freeing action_cpy directly caused an Invalid free error from valgrind since it was pointing into the middle of the allocated memory instead of the beginning.

You're welcome.