aacdec: Fix a brown paper bag bug.

aacdec: Fix a brown paper bag bug.

Oops, we were using PARA_MAX() instead of PARA_MIN() to determine
the number of bytes to convert in the next run.  This silly bug could
lead to a segfault in the aacdec filter. Moreover, the assertion in
buffer_tree.c that would have caught the bug was _also_ b0rken.

But it's not my fault. I blame Grover of the Sesame street for both
bugs. He did explain the difference between near and far, although
this knowledge is next to useless for a programmer. And he did not
say a single word about MIN and MAX, or true and false. No wonder
such bugs happen.