Don't save nonexistent files in the Projectile cache

[emdemir]

Expected behavior

The file would be only added to the Projectile when it's saved, or if it already exists when visited.

Actual behavior

When a file is visited, it is immediately added to the Projectile cache, which is annoying if you make a typo because then it keeps coming up in projectile-find-file unless you invalidate the cache, which also clears the MRU ordering.

Steps to reproduce the problem

1. Open a project that Projectile knows about
2. Visit a new file that doesn't exist

Environment & Version information

Doom v2.0.9 (9edd4f26f39fc1632d63aebd156ab028d222e733)
Branch: develop

Projectile version information

Projectile 2.2.0snapshot

Emacs version

GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)

Operating system

Debian bullseye/testing

[emdemir]

Note: it was suggested by hlissner from doomemacs/doomemacs#3423 to make an issue here.

[bbatsov]

Fixed in 7a3708f. projectile-cache-current-file now checks file-exists-p before adding to the cache, so visiting a new file and abandoning the buffer no longer leaves a ghost entry.