Johannes Schlatow 1c49da8ce4 terminal: don't overwrite last column until eol
Introduce a new _overflowed state variable to indicate whether the
horizontal boundary was reached already and to omit subsequent character
output.

This state is necessary to maintain a valid cursor position at all
times. The _overflowed attribute is reset once the cursor is moved into
a valid position again.

To harmonise the bounds checking for _cursor_pos modifications, the
`constrain()` method was added.

Fixes genodelabs/genode#4093

Also fixes a bug in `vpa()` and `vpb()` which moved the cursor
horizontally instead of vertically.
2021-05-05 11:35:27 +02:00
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