Redirection of thumbnail viewer's output to a file

[gardockt]

Currently, when a thumbnail viewer outputs something, such as an error, it writes to the display, messing up the interface. This is especially noticeable with asynchronous thumbnail loading, as trying to display a partially downloaded thumbnail prints an error (at least when using ueberzug). Another, more consistent way to reproduce this is to use imv and press p while its window is focused - a newline character is then printed. While this can be solved by redirecting viewer's output to a file, doing so also has some negative consequences.

Advantages:

• display is not messed up by viewer's output
• when debugging is needed, viewer's output can be read fully, with no characters getting overwritten (possibly low importance, as most significant error details can be read anyway)

Disadvantages:

• no direct indication of viewer throwing errors, which may result in viewer-related issue reports not containing potentially valuable information
• getting to read viewer's output is less convenient

(obviously, any other programs that ytfzf forks should be considered as well - thumbnail viewers may not be the only case)

What do you think about this change?

[Euro20179]

Maybe there could be some kind of variable like thumbnail_debug_log=/dev/null then it can be changed to /dev/stderr or something else if output is wanted.
It could have a companion option --thumbnail-log to set the variable.

[gardockt]

So I understand that having to ask for additional data in case of issues (which is probably the most important disadvantage) is not a problem - I can create a pull request in a few hours.

[Euro20179]

Asking for more data is not really a problem, as I can simply ask them to run ytfzf --thumbnail-log=/dev/stdout.

Also, there is no need for a pull request as I have already implemented this :)