Relax type checking when fuction position is nil

This lets the flychecker work as expected.

src/core/compile.c

@@ -454,6 +454,7 @@ static JanetSlot janetc_call(JanetFopts opts, JanetSlot *slots, JanetSlot fun) {
                 break;
                 case JANET_CFUNCTION:
                 case JANET_ABSTRACT:
+                case JANET_NIL:
                     break;
                 case JANET_KEYWORD:
                     if (min_arity == 0) {

test/suite7.janet

@@ -182,4 +182,6 @@
 (assert (= (string out-buf) "Hello\nhi") "print and prin to buffer 1")
 (assert (= (string err-buf) "Sup\nnot much.") "eprint and eprin to buffer 1")
 
+(assert (= (string '()) (string [])) "empty bracket tuple literal")
+
 (end-suite)