Remove all strcmp and strlen calls on Glyph.c[]

Remove all strcmp and strlen calls on Glyph.c[]

There were a few occurrences of strcmp and strlen being called on Glyph.c[],
which is not always null-terminated (this actually depends on the last values in
the buffer s in ttyread()). This patch replace all the calls to strcmp with a
test on c[0] directly or a call to tlinelen, and the one to strlen with utf8len.
I also took the opportunity to refactor getsel and tdumpline.

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>