Perl: avoid returning 500 if header was already sent. Returning NGX_HTTP_INTERNAL_SERVER_ERROR if a perl code died after sending header will lead to a "header already sent" alert. To avoid it, we now check if header was already sent, and return NGX_ERROR instead if it was.

--- a/src/http/modules/perl/nginx.xs
+++ b/src/http/modules/perl/nginx.xs
@@ -164,6 +164,8 @@ send_http_header(r, ...)
         }
     }
 
+    ctx->header_sent = 1;
+
     r->disable_not_modified = 1;
 
     rc = ngx_http_send_header(r);