Silenced a warning for some compilers.

src/core/ngx_resolver.c

diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c
index 11f66ee..d4af2f0 100644
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -1236,6 +1236,7 @@
     addrs = NULL;
     cname = NULL;
     qtype = 0;
+    ttl = 0;
 
     for (a = 0; a < nan; a++) {