Get one byte (8-bit) of the program at 'ea' from the database
even if the debugger is active.
ea - linear address
returns: byte value. If the byte has no value then 0xFF is returned.
If the current byte size is different from 8 bits, then the returned value
may have more 1's.
To check if a byte has a value, use is_loaded(ea)
long get_db_byte(long ea); // get a byte at ea