Unhandled escape sequences clobber tbot output

[Rahix]

I've seen a shell send the following escape sequences which tbot doesn't handle well:

│   ├─(690600)< '\x1b7\x1b[r\x1b[999;999H\x1b[6n'

Individually, these mean:

Sequence	Meaning
\x1b7	Save Cursor (DECSC)
\x1b[r	?
\x1b[999;999H	Cursor Position [row;column] (default = [1,1]) (CUP)
\x1b[6n	Report Cursor Position (CPR) [row;column]