fix segfault in resolver:
ngx_resolve_name_done() and ngx_resolve_addr_done() did not delete
contexts from a resolver node waiting list.

src/core/ngx_resolver.c

diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c
index 9adc2d2..82785c2 100644
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -464,6 +464,7 @@
 
             ctx->next = rn->waiting;
             rn->waiting = ctx;
+            ctx->state = NGX_AGAIN;
 
             return NGX_AGAIN;
         }
@@ -625,6 +626,7 @@
 
             ctx->next = rn->waiting;
             rn->waiting = ctx;
+            ctx->state = NGX_AGAIN;
 
             /* unlock addr mutex */