Fixed invoking functions within function arguments

Somewhat similar to c9d4b9965c

tests/scripts/test_function_invocation_in_arguments.toy

@@ -0,0 +1,11 @@
+
+
+fn a(x) {
+	assert x == 42;
+}
+
+fn b() {
+	return 42;
+}
+
+a(b());

tests/scripts/test_keyword_pass.toy

@@ -0,0 +1 @@
+pass;

tests/scripts/test_keyword_return.toy

@@ -0,0 +1,8 @@
+
+fn empty() { //BUG: there's an extra return in the bytecode
+	return;
+}
+
+fn full() {
+	return 42;
+}