patch 8.2.4755: cannot use <SID>FuncRef in completion spec

Problem:    Cannot use <SID>FuncRef in completion spec.
Solution:   Dereference a function name in another way. (closes #10197)
diff --git a/src/eval.c b/src/eval.c
index 90ed14b..cad6887 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -639,7 +639,15 @@
 
     ref.v_type = VAR_UNKNOWN;
     if (eval7(arg, &ref, evalarg, FALSE) == FAIL)
-	return NULL;
+    {
+	dictitem_T	*v;
+
+	// If <SID>VarName was used it would not be found, try another way.
+	v = find_var_also_in_script(name, NULL, FALSE);
+	if (v == NULL)
+	    return NULL;
+	copy_tv(&v->di_tv, &ref);
+    }
     if (*skipwhite(*arg) != NUL)
     {
 	if (verbose)