failed to decode envelope: unexpected end of JSON input

[GeertJohan]

Errors like these may occur in the standard output:

go-flutter: failed to pop route after escape key press: failed to decode envelope: unexpected end of JSON input

This is the case because InvokeMethod always expects a response which it wants to decode, but we don't always get a response. Currently responses are not implemented (flutter/flutter#18852), and even when they are, some methods don't return a response.

Java has InvokeMethod vs InvokeMethod with callback. Perhaps we should also provide two methods, one which doesn't expect a response and therefore doesn't try to decode it (resulting in decode error)

[pchampio]

fix taged in tag: v0.29.0