Adventure fails to convert old sign text properly

[JRoy]

Issue Summary

A sign created with text §1[Buy] on Paper build 472 (build right before adventure) produces the following NBT for Text1:

{"extra":[{"bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false,"color":"dark_blue","text":"[Buy]"}],"text":""}

A sign created with text §1[Buy] on latest Paper build produces the following NBT for Text1:

{"color":"dark_blue","text":"[Buy]"}', Text2: '{"text":"1"}

When using Sign#getLine(int) (converts to legacy string), Paper 472 will convert the both of the above components to §1[Buy] which is the "correct" legacy string representation.

However, using Sign#getLine(int) with the first component on the latest Paper, it will produce §1[Buy]§r. This may be the correct way to convert the component but we shouldn't being doing this in order to maintain compatibility with (the broken I guess) upstream component conversion.

[kashike]

This should be fixed as of 27a8d99 and 7f72c46.