pad: Fix bug in function getStages()

In cases where the pad had no stages beneath it, `new
stage($this->stage)` would construct an invalid object.  As it turns
out, calling ->getArray() on an uninitialized stage object yeilds bad
results.

Instead of patching the stage::getArray() function, I add a check to
harden pad::getStages().  My reasoning for this is as follows:  The bug
in getArray() manifests from a domain error, ie. it's only because we
are calling it on an uninitialized object.  The object is already in a
bad state prior to caling getArray().  Rather, I opt to patch
getStages() so that we never create a bad object in the first place.

Now, for no-stage pads, getStages() will return early an empty array.

0 files changed, 0 insertions, 0 deletions