Make the node path relative to the target node instead of the source node.
Currently, a proxy object is used in the connection dialog to edit bound arguments.
In this case, the `EditorPropertyNodePath` will get the node path relative to the
source object in the connection (i.e. the object the InspectorDock is editing).
This path is not available in scripts (i.e. the target object in the connection).
When a Signal with unbinds was connected to a non-existing function, the connection attempt was made before the function was created.
I moved the creation of the function in front of the connection attempt.
