FastCGI: fixed wrong connection close with fastcgi_keep_conn.

With fastcgi_keep_conn it was possible that connection was closed after
FCGI_STDERR record with zero padding and without any further data read yet.
This happended as f->state was set to ngx_http_fastcgi_st_padding and then
"break" happened, resulting in p->length being set to f->padding, i.e. 0
(which in turn resulted in connection close).

Fix is to make sure we continue the loop after f->state is set.

src/http/modules/ngx_http_fastcgi_module.c

diff --git a/src/http/modules/ngx_http_fastcgi_module.c b/src/http/modules/ngx_http_fastcgi_module.c
index 123125a..5e8ef40 100644
--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -1788,10 +1788,6 @@
                               "FastCGI sent in stderr: \"%*s\"",
                               m + 1 - msg, msg);
 
-                if (f->pos == f->last) {
-                    break;
-                }
-
             } else {
                 if (f->padding) {
                     f->state = ngx_http_fastcgi_st_padding;