Problem:    Repeating line comment is undesired for "O" command.
Solution:   Do not copy line comment leader for "O". (closes #9426)

Problem:    After ":cd" fails ":cd -" is incorrect.
Solution:   Set the previous directory only after successfully changing
            directory. (Richard Doty, closes #9419, closes #8983)

Problem:    C line comment not formatted properly.
Solution:   If a line comment follows after "#if" the next line is not the end
            of a paragraph.

Problem:    Coverity reports a memory leak.
Solution:   Free memory in case of failure.

Problem:    getcmdline() argument has a misleading type.
Solution:   Use the correct type, even though the value is not used.

Problem:    Using unititialized variable.
Solution:   Set the option flags to zero for a terminal option.

Problem:    Heredoc test fails.
Solution:   Correct order of function arguments.

Problem:    Vim9: double free when using lambda.
Solution:   Don't free both cmdline and line_to_free.

Problem:    Build failure without the 'autochdir' option. (John Marriott)
Solution:   Add #ifdefs.

Problem:    Diff mode confused by NUL bytes.
Solution:   Handle NUL bytes differently. (Christian Brabandt, closes #9421,
            closes #9418)