Fixed segfault with filter_finalize introduced in r4621 (1.3.0).

Example configuration to reproduce:

    location /image/ {
        error_page 415 = /zero;
        image_filter crop 100 100;
        proxy_pass http://127.0.0.1:8080;
        proxy_store on;
    }

    location /zero {
        return 204;
    }

The problem appeared if upstream returned (big enough) non-image file,
causing 415 to be generated by image filter.
diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index fa58dd9..06f89d6 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -1933,8 +1933,6 @@
 
     if (rc == NGX_OK && r->filter_finalize) {
         c->error = 1;
-        ngx_http_finalize_connection(r);
-        return;
     }
 
     if (rc == NGX_DECLINED) {