Fix #76943: Inconsistent stream_wrapper_restore() errors

[cmb69]

If restoring of any not registered built-in wrapper is requested, the
function is supposed to fail with a warning, so we have to check this
condition first.

Furthermore, to be able to detect whether a built-in wrapper has been
changed, it is not sufficient to check whether any userland wrapper
has been registered, but rather whether the specific wrapper has been
modified.

[ohader]

How would it possible to determine whether a different stream wrapper has been registered?

stream_wrapper_restore() does not only restore unregistered (non-existing) stream wrappers, but it also reverts alternativ stream wrapper implementations back to PHP's native stream wrapper. stream_get_wrappers() just tells, whether a wrapper is registered - but it does not tell, whether it's PHP's native implementation or a custom stream wrapper.

With this change, the only way to overcome notices is to mute error output @stream_wrapper_restore().
Thanks in advance for hints or thoughts on this topic!

[cmb69]

How would it possible to determine whether a different stream wrapper has been registered?

It seems to me this functionality is missing; something like stream_wrapper_get_registered($protocol) which returns the registered class name or null appears to be useful.