runtime: Return OPEN also if already open
runtime: Return OPEN also if already open

Caused issue when connecting to microcontroller which was
already running (and noone had sent EOT). Host was then not
getting a response as expected, and got stuck

microflo/microflo,microflo/microflo,microflo/microflo,microflo/microflo,microflo/microflo,rraallvv/microflo,rraallvv/microflo,rraallvv/microflo,rraallvv/microflo,microflo/microflo