patch 8.2.0559: clearing a struct is verbose

Problem:    Clearing a struct is verbose.
Solution:   Define and use CLEAR_FIELD() and CLEAR_POINTER().
diff --git a/src/search.c b/src/search.c
index e3265c2..8c335ff 100644
--- a/src/search.c
+++ b/src/search.c
@@ -470,7 +470,7 @@
     if (len)
 	memcpy(lastc_bytes, s, len);
     else
-	vim_memset(lastc_bytes, 0, sizeof(lastc_bytes));
+	CLEAR_FIELD(lastc_bytes);
 }
 #endif