Fix unicode support in db(1).
command() receives a char* that is assigned to lp, which is a Rune*,
and lp is incremented later in readchar(), so each read consumed 4 bytes.
The only time command() is called is in runpcs() with bkpt->comm,
which is a char* built in subpcs through a char*, so the string stored in
bkpt->comm was not a Rune string. A way to test the bug is:

db program
main:b argv/X
:r