[Request] Add description for error 50

[phol]

Is your feature request related to a problem? Please describe.

Unfortunately for me, but fortunately for the OpenDTU project, the grid instability I'm facing got me another error unknown by OpenDTU: Alarm code 50. Once again, I sent a message to Hoymiles for clarification.

Describe the solution you'd like

Add description for code 50.

This time, their answer is a bit cryptic, but this is what I received as description:

"The 50 code is the praevia alarming of FB over-current protection failure. And it is also cause by the unstable grid voltage."