patch 9.0.2030: no max callback recursion limit

Problem:  no max callback recursion limit
Solution: bail out, if max call recursion for callback functions
          has been reached.

This checks the 'maxfuncdepth' setting and throws E169 when a callback
function recursively calls itself.

closes: #13337
closes: #13339

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/userfunc.c

@@ -3583,6 +3583,13 @@ call_callback(
 
     if (callback->cb_name == NULL || *callback->cb_name == NUL)
 	return FAIL;
+
+    if (callback_depth > p_mfd)
+    {
+	emsg(_(e_command_too_recursive));
+	return FAIL;
+    }
+
     CLEAR_FIELD(funcexe);
     funcexe.fe_evaluate = TRUE;
     funcexe.fe_partial = callback->cb_partial;