error behavior improved and TAB character handled. Refs: #182.
1. Selecting a font not in the font table now returns the default font.
This is because LibreOffice sometimes selects an undefined font but does not use it at all.
The new behavior avoids a TRAP 100 in such cases.
3. 09X (TAB) is no longer ignored. This is used for example in VS Editor.
3. Reference to RTF specification added in header comment.

Signed-off-by: Josef Templ <josef.templ@gmail.com>