Add bounds check in SoftAACEncoder2::onQueueFilled()

Original code blindly copied some header information into the
user-supplied buffer without checking for sufficient space.
The code does check when it gets to filling the data -- it's
just the header copies that weren't checked.

Bug: 34617444
Test: ran POC before/after
Change-Id: I6e80ec90616f6cd02bb8316cd2d6e309b7e4729d
(cherry picked from commit 62312436)