Fix new function: fopenlog()

ftello() returns 0 after fnopen(..., O_APPEND). Use filelength() instead.
14 jobs for dailybuild_linux-x64 in 10 minutes and 23 seconds (queued for 16 seconds)
Status Job ID Name Coverage
  Build
passed #34619
FreeBSD
jsdoor-freebsd

00:04:13

passed #34620
Linux
jsdoor-linux

00:07:04

passed #34622
FreeBSD
jsdoor-windows

00:02:05

passed #34614
FreeBSD
sbbs-freebsd

00:05:55

passed #34609
Linux
sbbs-linux

00:09:54

passed #34612
Windows
sbbs-windows

00:04:54

passed #34621
FreeBSD
sexpots-freebsd

00:00:13

passed #34610
Linux
sexpots-linux

00:00:20

passed #34613
Windows
sexpots-windows

00:00:22

passed #34617
FreeBSD
syncdraw-freebsd

00:00:25

passed #34618
Linux
syncdraw-linux

00:01:01

passed #34615
FreeBSD
syncterm-freebsd

00:01:06

passed #34611
Linux
syncterm-linux

00:03:00

passed #34616
FreeBSD
syncterm-windows

00:01:55