Failed parsing of signed message

[sosnovsky]

Browser extension fails to parse signed message with attached signature

@ioanmo226 please work on this issue after finishing your current one, I forwarded you email with attached .eml

[sosnovsky]

@ioanmo226 let's check if node name is equal to signature.asc (like we do in iOS - https://github.com/FlowCrypt/flowcrypt-ios/blob/master/Core/source/core/att.ts#L89)