Indenting/unindenting always happens in a single contiguous block.
Lines that cannot or should not be indented or unindented do not
need to remembered separately as it follows from their content.

Suggested-by: Brand Huntsman <alpha@qzx.com>

This fixes https://savannah.gnu.org/bugs/?53532.

To prevent any filenames containing hyphens getting partially colored.
Reported-by: Brand Huntsman <alpha@qzx.com>

Put it after the function that it calls, and before the functions
it is called from.

That is, do not fall back to the default background color when the
name for the background color is invalid, but reject the entire
color command, just like for an invalid foreground color.

Also add some comments, and accept hyphens in function names.

This allows a syntax to remove the color from things that were colored
overeagerly by earlier regexes.

This fixes https://savannah.gnu.org/bugs/?53445.

Also, reshuffle a condition so it takes up less space.

This variable will be modified by go_forward_chunks(), but the value
of openfile->current itself should be maintained.

An "if possible" would have been nice, but there is no room for that.

This will make the tiny version slightly smaller.

This avoids eleven warnings of the kind "comparison between signed
and unsigned integer expressions [-Wsign-compare]".

In the preceding commit, open_buffer() was changed so that it gets
told whether to load into a new buffer or not, so it is no longer
needed to convey this information through a flag.

And also prevent a theoretical crash for restricted prompt functions.

This fixes a regression introduced by commit 54103d8e: a crash that
can be triggered by running 'nano --restrict' and pressing <Insert>.

This addresses https://bugzilla.redhat.com/1558532.