Failures if connection objects created before all audio objects created

[PaulStoffregen]

Details here:

https://forum.pjrc.com/threads/29582-Audio-library-co-existence-of-a-waveform-synthesis-object-and-an-FFT-object?p=81132&viewfull=1#post81132

[mamuesp]

In case of creation by the GUI, the connection objects will be placed at the end of all automatically defined objects. And it's obvious that they might only work if the corresponding input/output obejcts exists - the AudioConnection is referencing the other objects, a "null" avlue at this place is not very helpful.