Valid unknown application extensions are parsed incorrectly

[follower]

AFAICT this is not a valid way to skip unknown application extensions:

x-gif/src/exploder.js

Lines 64 to 65 in 085b0c7

	streamReader.log("A weird application extension. Skip until we have 2 NULL bytes");
	while (!(streamReader.readByte() === 0 && streamReader.peekByte() === 0));

This is because:

1. Sub-block data of the extension could contain two consecutive zeros.
2. AFAICT there's no requirement for application extensions to end with 0x00 0x00 (See: http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp#plain_text_extension_block. While the NETSCAPE2.0 extension happens to end with 0x00 0x00 only the final 0x00 is considered the block terminator. ). I think the correct approach is to read sub-block sizes and skip each sub-block until the size is 0 (as is done elsewhere).