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]
diff --git a/src/dumpstats.c b/src/dumpstats.c
index b35a5a8..dd017e1 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -4462,7 +4462,7 @@
 		unsigned int prev_len = si->ib->buf->i;
 		unsigned int data_len;
 		unsigned int last_len;
-		unsigned int last_fwd;
+		unsigned int last_fwd = 0;
 
 		if (appctx->ctx.stats.flags & STAT_CHUNKED) {
 			/* One difficulty we're facing is that we must prevent