Math Node UI (Bug Fix)

Fixed two bugs found after merging:

1. Opened the Math node inspector without editing
anything, then clicked somewhere else on the page,
it crashed.

2. Similarly, opened the Math node inspector
without editing anything, then clicked the
"Cancel" button to cancel the edit, it crashed.

Both of these problems are fixed by this patch.
The issue was with using the getFocusedNode() in
the inspector onClose function to save changes.

Also, I included some minor changes relating to
the last code review. =D

Change-Id: I6e200f2a228b71dc5af5aa9843c461f43b926f8d
Merge "Math Node UI (Bug Fix)"