patch 8.2.3100: Vim9: no error when using type with unknown number of args

Problem:    Vim9: no error when using type with unknown number of arguments.
Solution:   Do not ignore argument count of -1. (closes #8492)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index e635116..ec74fde 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2055,6 +2055,18 @@
 }
 
 /*
+ * Get the argument count for function "idx".
+ * "argcount" is the total argument count, "min_argcount" the non-optional
+ * argument count.
+ */
+    void
+internal_func_get_argcount(int idx, int *argcount, int *min_argcount)
+{
+    *argcount = global_functions[idx].f_max_argc;
+    *min_argcount = global_functions[idx].f_min_argc;
+}
+
+/*
  * Call the "f_retfunc" function to obtain the return type of function "idx".
  * "argtypes" is the list of argument types or NULL when there are no
  * arguments.