[BUG] Stream overflow detection not working correctly

[Paciente8159]

Describe the bug
When you write more chars to the buffer then the available capacity the overflow error is not being triggered properly.
Most of the times this is not an issue since streamers keep track of the characters sent.

What is your hardware
N/A

What was the GCode running
N/A

Screenshots
N/A

Additional context
Buffer write is preventing the OVF char from being written.