desktop-exports: ensure we have $HOME/.config dir

[3v1n0]

Create it if it doesn't exist, otherwise next operations will fail

I was just running a snap, while I noticed:

marco@tricky:/data/telegram-snap (master):✓ $ mailspring 
/snap/mailspring/216/bin/desktop-launch: line 177: /home/marco/snap/mailspring/common/.config/user-dirs.dirs: No such file or directory
cp: cannot create regular file '/home/marco/snap/mailspring/common/.config/': Not a directory
/snap/mailspring/216/bin/desktop-launch: line 180: /home/marco/snap/mailspring/common/.config/user-dirs.dirs.md5sum: No such file or directory
/snap/mailspring/216/bin/desktop-launch: line 180: /home/marco/snap/mailspring/common/.config/user-dirs.locale.md5sum: No such file or directory

[kenvandine]

This looks good to me

[oSoMoN]

The test looks superfluous, given that "mkdir -p" will silently do nothing if the directory already exists.

[3v1n0]

@oSoMoN yeah, not really harmful though... I get rid of it if you prefer.

[oSoMoN]

LGTM, thanks!