obs_data:  Fix wrong data queried for release

On release of obs_data, if the default/autoselect values pointed toward
a sub-object or a sub-array, it would look up the data for the regular
user value.  (Palana must have forgot to change these functions around
when adding the default/autoselect functionality)
Fix obs_data_item_setdata

It would try to move data from the old pointer even if the pointer was
changed via realloc, which would cause it to copy data from freed
memory.  Instead, just get the position of the data and call memmove to
move it up.
Always create new object when setting a sub-object

Do not use the object returned from obs_data_get_obj to set new
settings.  It could be the default object, which means you'd just end up
modifying the default data, which won't get saved.  Always create a new
object when setting sub-object data.  It doesn't particularly hurt
anything.