fix: check if file exists before deleting

[LuanGB]

fixes #1073

[unixmonkey]

FYI, this issue also may exist here: https://github.com/mileszs/wicked_pdf/blob/master/lib/wicked_pdf.rb#L46-L50 where the files are closed without checking they exist first.

I'm curious how this is a new problem after the upgrade though... It seems that if any other process clearing tempfiles (a deploy maybe?) could cause this to happen in both old and new versions.

It might also be nice to delete or preserve the header & footer tempfiles with that same :delete_temporary_files option and call close or close! based on it.

[LuanGB]

I'm suspecting that this may be related to this PR: #1039
Cannot put my finger on what exactly is causing it, however

[unixmonkey]

BTW, although it is very tiny, there could be a race-condition where the file exists while checking if the file exists and deleting it. Maybe it'd be better if closing a tempfile were rescue-able than checking for existence. Should speed things up too.

[LuanGB]

That's a good idea. I'll put something together soon.

[unixmonkey]

Ping.

[alex-kovshovik]

I ran into the same issue, probably will have to use the forked version until this fix is released.