swap mkdir and is_dir in check to prevent php errors

[rmpel]

possible solution for https://github.com/kalessil/phpinspectionsea/issues/1847

I THINK this should do it, but, I have no idea how to compile the plugin and use it in phpStorm.

maybe there needs to be some work done around line 120, as that's where another check is for the presence of is_dir is, however; does it check for the position (before or after mkdir) as well???

[rmpel]

hehe, don't know ;) as said, I have no way to test it. I'll commit your suggestions, but it is up to the maintainer to test/debug, or someone help me set-up a working compile + test in phpStorm, then I can debug it myself (I hope)