overworked coverage

src/json.hpp.re2c

@@ -3629,7 +3629,7 @@ class basic_json
                 re2c:define:YYCURSOR = m_cursor;
                 re2c:define:YYLIMIT  = m_limit;
                 re2c:define:YYMARKER = m_marker;
-                re2c:define:YYFILL   = "{ yyfill(); }";
+                re2c:define:YYFILL   = "yyfill(); // LCOV_EXCL_LINE";
                 re2c:yyfill:parameter = 0;
                 re2c:indent:string   = "    ";
                 re2c:indent:top      = 1;