avifil32: Fix some memory leaks

[Andrew Talbot]

Paul Vriens wrote:

> Doesn't this mean that every one of those 4 mmio-calls are executed? In
> the previous logic we would bail out after one failure.
> 

My reasoning is that short-circuit evaluation ensures that expressions are
evaluated from left to right, and as soon as one evaluates as true, the
whole "if" clause must be true, so the remaining statements are discarded.

-- 
Andy.