BUILD: stats: let gcc know that last_fwd cannot be used uninitialized...

OK, for once it cannot easily know this one, and certain versions are
emitting this harmless warning :

  src/dumpstats.c: In function 'http_stats_io_handler':
  src/dumpstats.c:4507:19: warning: 'last_fwd' may be used uninitialized in this function [-Wmaybe-uninitialized]
1 file changed