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/search.c b/src/search.c
index 1e4464b..74ca8fe 100644
--- a/src/search.c
+++ b/src/search.c
@@ -3202,7 +3202,7 @@
     proftime_T  start;
 #endif
 
-    vim_memset(stat, 0, sizeof(searchstat_T));
+    CLEAR_POINTER(stat);
 
     if (dirc == 0 && !recompute && !EMPTY_POS(lastpos))
     {