Avoid CLI issues

[oliverturner]

I added an early return if the environment isn't the browser to not throw errors when running composer updates etc.

[oliverturner]

Oops... looks as though I accidentally reformatted, causing a ton of "changes".

The only genuine adjustment is a single statement on line 115

[JosephLenton]

There is a better place to do this, where PHP Error should be disabled or not, and so I've added it there.

I also worry that leaving early might leave the error handling functions/classes undefined, which would cause random errors if you had calls left inside a script, expecting them to do nothing.