patch 8.2.5107: some callers of rettv_list_alloc() check for not OK

Problem:    Some callers of rettv_list_alloc() check for not OK. (Christ van
            Willegen)
Solution:   Use "==" instead of "!=" when checking the return value.
diff --git a/src/cmdexpand.c b/src/cmdexpand.c
index c3731cb..28ecaed 100644
--- a/src/cmdexpand.c
+++ b/src/cmdexpand.c
@@ -3754,7 +3754,7 @@
     else
        pat = addstar(xpc.xp_pattern, xpc.xp_pattern_len, xpc.xp_context);
 
-    if ((rettv_list_alloc(rettv) != FAIL) && (pat != NULL))
+    if (rettv_list_alloc(rettv) == OK && pat != NULL)
     {
 	int	i;