[nga-c] corrected fix for script:name (issue #99)

FossilOrigin-Name: eca3b588f990932f2161d869df338c8cb4f96bd17b13a1fcd741526661ea3e4a

RELEASE-NOTES

@@ -53,6 +53,7 @@
   - new "-p" option to run non-Unu format source files
   - now report "<none>" for `script:name` if no file is being
     run
+  - now report 0 for `script:arguments` if not running a program
 
 Future Notes
 

vm/nga-c/retro.c

@@ -551,7 +551,10 @@ V scripting_arg(NgaState *vm) {
 }
 
 V scripting_arg_count(NgaState *vm) {
-  stack_push(vm, vm->sys_argc - 2);
+  if ((vm->sys_argc - 2) <= 0)
+    stack_push(vm, 0);
+  else
+    stack_push(vm, vm->sys_argc - 2);
 }
 
 V scripting_include(NgaState *vm) {
@@ -563,7 +566,7 @@ V scripting_include_plain(NgaState *vm) {
 }
 
 V scripting_name(NgaState *vm) {
-  if ((vm->sys_argc - 2) <= 0)
+  if (vm->sys_argc == 1)
     stack_push(vm, string_inject(vm, "<none>", stack_pop(vm)));
   else
     stack_push(vm, string_inject(vm, vm->sys_argv[1], stack_pop(vm)));