FastCGI: f->split_parts reset on request start.

Additionally, make sure to check for errors from ngx_http_parse_header_line()
call after joining saved parts.  There shouldn't be any errors, though
check may help to catch bugs like missing f->split_parts reset.

Reported by Lucas Molas.

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 24dbbf6..80cd1a2 100644
--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -1208,6 +1208,10 @@
     f->fastcgi_stdout = 0;
     f->large_stderr = 0;
 
+    if (f->split_parts) {
+        f->split_parts->nelts = 0;
+    }
+
     r->state = 0;
 
     return NGX_OK;
@@ -1488,6 +1492,13 @@
 
                     rc = ngx_http_parse_header_line(r, &buf, 1);
 
+                    if (rc != NGX_OK) {
+                        ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
+                                      "invalid header after joining "
+                                      "FastCGI records");
+                        return NGX_ERROR;
+                    }
+
                     h->key.len = r->header_name_end - r->header_name_start;
                     h->key.data = r->header_name_start;
                     h->key.data[h->key.len] = '\0';