Fix possible negative offset to fseeko()

CID 350353
14 jobs for master in 9 minutes and 29 seconds (queued for 15 seconds)
Status Job ID Name Coverage
  Build
passed #32336
FreeBSD
jsdoor-freebsd

00:04:08

passed #32337
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jsdoor-linux

00:06:35

passed #32339
FreeBSD
jsdoor-windows

00:01:55

passed #32331
FreeBSD
sbbs-freebsd

00:05:38

passed #32326
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sbbs-linux

00:09:26

passed #32329
Windows
sbbs-windows

00:05:42

passed #32338
FreeBSD
sexpots-freebsd

00:00:10

passed #32327
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sexpots-linux

00:00:14

passed #32330
Windows
sexpots-windows

00:00:30

passed #32334
FreeBSD
syncdraw-freebsd

00:00:24

passed #32335
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syncdraw-linux

00:00:58

passed #32332
FreeBSD
syncterm-freebsd

00:01:03

passed #32328
Linux
syncterm-linux

00:02:52

passed #32333
FreeBSD
syncterm-windows

00:01:45