patch 9.0.1391: "clear" macros are not always used

Problem:    "clear" macros are not always used.
Solution:   Use ALLOC_ONE, VIM_CLEAR, CLEAR_POINTER and CLEAR_FIELD in more
            places. (Yegappan Lakshmanan, closes #12104)
diff --git a/src/quickfix.c b/src/quickfix.c
index 63dd541..13292e2 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -6213,7 +6213,7 @@
 {
     char_u	*p;
 
-    vim_memset(args, 0, sizeof(*args));
+    CLEAR_POINTER(args);
 
     args->regmatch.regprog = NULL;
     args->qf_title = vim_strsave(qf_cmdtitle(*eap->cmdlinep));