Minor Simplifications

[simlu]

parallelgzip/src/main/java/org/anarres/parallelgzip/ParallelGZIPOutputStream.java

Lines 234 to 239 in de135ec

	Block b = freeBlock;
	if (b != null)
	freeBlock = null;
	else
	b = new Block();
	block = b;

How about

        block = freeBlock == null ? new Block() : freeBlock;
        freeBlock = null;

Shorter and more understandable.

Also the first throw exception is unnecessary.

Created a PR here: #10