Fix _NARG crashing outside of macros

And add a test for it

src/asm/symbol.c

@@ -77,6 +77,10 @@ void sym_ForEach(void (*func)(struct Symbol *, void *), void *arg)
 
 static int32_t Callback_NARG(void)
 {
+	if (!macro_GetCurrentArgs()) {
+		yyerror("_NARG does not make sense outside of a macro");
+		return 0;
+	}
 	return macro_NbArgs();
 }
 

test/asm/narg-nosect.asm

@@ -0,0 +1 @@
+	PRINTT "{_NARG}\n"

test/asm/narg-nosect.err

@@ -0,0 +1,3 @@
+ERROR: narg-nosect.asm(1):
+    _NARG does not make sense outside of a macro
+error: Assembly aborted (1 errors)!

test/asm/narg-nosect.out

@@ -0,0 +1 @@
+$0