kino/filehandler.cc: check return value from lseek()

kino/filehandler.cc: check return value from lseek()

Fixes Coverity CID 709329: Unchecked return value (CHECKED_RETURN)
Calling function "lseek" without checking return value (as is done elsewhere 19 out of 20 times).
No check of the return value of "lseek(this->fd, 0L, 0)".
409        lseek( fd, 0, SEEK_SET );