log: measure the debug log with a size type that can hold it

GetFilesize() returned int while ftell() returns long, so a debug.log of
2 GiB or more came back negative. Its only caller is the -maxdebugfilesize
roll added in ae1c6a7, which skips the roll on a negative size: the
rotation written for issue #34 would have switched itself off permanently
at exactly the size it exists to prevent. Production was at 1.95 GiB
growing 51-129 MB/day, about a day short of crossing 2 GiB.

The same truncation capped the comparison at INT_MAX (2047.99 MB), so
-maxdebugfilesize=2048 or higher could never be exceeded and disabled
rotation outright. Both failures were silent.

Widen the return to int64 and seek with ftello/fseeko (_ftelli64 and
_fseeki64 on Windows). The roll in util.h is the function's only caller
in the tree, so no other behaviour changes. A 32-bit off_t would
reintroduce the same truncation, so its width is now a compile-time
assertion rather than a silent runtime surprise.

0 files changed, 0 insertions, 0 deletions