Invalid files silently succeed

[emosenkis]

Most invalid files silently succeed, producing Text, Start, and Eof events (others are probably possible too).

Examples:

• The empty file (produces just Eof)
• foo (produces Text followed by Eof)
• < (produces Start(BytesStart { buf: [], name_len: 0 }), followed by Eof)
• <foo> (produces Start, Eof)

[tafia]

The empty file (produces just Eof)

I think this is a correct behavior.

For the rest I agree we should add additional checks on event orders.

[Mingun]

All things except < are parsed correctly, but it is possible to add a setting to return IllFormed error in those cases. Invalid parsing of < will be fixed in #622.