Eo add ref: Fix a bug causing leaks and wrong refcount in some cases.

Eo add ref: Fix a bug causing leaks and wrong refcount in some cases.

When using eo_add_ref, it was increasing the refcount before the user
context in the addition has fully ended. This means the object had its
reference increased while still not finalized, which means it was
sometimes passed with an increased refcount to unsuspecting class code.
The correct behaviour is to increase the reference count just before
returning the object to the user at the end of eo_add so the reference
count is only increased for whoever asked for it.

Breaks ABI!

@fix