There is a difference between empty/default (change value to default)
and none (don't modify), so make this explicit for some PlaceObject
parameters where it wasn't.
Fixes#1104.
Some SWFs are compressed incorrectly, often with incorrect
compressed/uncompressed lengths, causing the zlib decoders
to vomit if you try to decompress them fully. However, often times
the data still decompresses all the way to the End tag, and we
still want to try to play it even if it's corrupt.
Now these errors only omit a warning, and we'll continue to run
the SWF.
Addresses #86.