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/evalbuffer.c b/src/evalbuffer.c
index 7de7271..0808c7e 100644
--- a/src/evalbuffer.c
+++ b/src/evalbuffer.c
@@ -680,7 +680,7 @@
     int		sel_bufloaded = FALSE;
     int		sel_bufmodified = FALSE;
 
-    if (rettv_list_alloc(rettv) != OK)
+    if (rettv_list_alloc(rettv) == FAIL)
 	return;
 
     if (in_vim9script()