patch 9.0.0444: trying to declare g:variable gives confusing error

Problem:    Trying to declare g:variable gives confusing error.
Solution:   Give a better error message. (closes #11108)
diff --git a/src/eval.c b/src/eval.c
index f208ab1..5d93b7e 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1031,12 +1031,16 @@
 	    {
 		char_u	    *tp = skipwhite(p + 1);
 
+		if (is_scoped_variable(name))
+		{
+		    semsg(_(e_cannot_use_type_with_this_variable_str), name);
+		    return NULL;
+		}
 		if (tp == p + 1 && !quiet)
 		{
 		    semsg(_(e_white_space_required_after_str_str), ":", p);
 		    return NULL;
 		}
-
 		if (!SCRIPT_ID_VALID(current_sctx.sc_sid))
 		{
 		    semsg(_(e_using_type_not_in_script_context_str), p);