Fixed $content_length cacheability with chunked (ticket #2252).

src/http/ngx_http_variables.c

diff --git a/src/http/ngx_http_variables.c b/src/http/ngx_http_variables.c
index c25d80c..942dacd 100644
--- a/src/http/ngx_http_variables.c
+++ b/src/http/ngx_http_variables.c
@@ -1179,6 +1179,10 @@
         v->no_cacheable = 0;
         v->not_found = 0;
 
+    } else if (r->headers_in.chunked) {
+        v->not_found = 1;
+        v->no_cacheable = 1;
+
     } else {
         v->not_found = 1;
     }