Adds new exists logic that can optionally ignore the file extension

[Lagicrus]

Fixes #5147

Adds a new setting to the configuration that, when enabled (default false), will use glob to check if that file exists with any file extension.
This means that during the pre-download phase when the path.exists function is called.
Where before, when it checked to see if ./random/path/to/image_5.jpg exists on the disk and it only finds ./random/path/to/image_5.png, it will return False as the file extension does not match.
With this tweak, it will return True as the path + name match as the file extension is ignored.