Check cloud serial is initialized before use
Check cloud serial is initialized before use

The cloud serial read, write and peek functions did not check whether
begin() had been called first. If not, the read/write/peek would lock up
the ESP8266 with a fatal exception.

digistump/OakCore,pfeerick/OakCore,digistump/OakCore,pfeerick/OakCore,digistump/OakCore,digistump/OakCore,pfeerick/OakCore,pfeerick/OakCore,pfeerick/OakCore,digistump/OakCore