patch 8.2.0572: using two lines for free and reset

Problem:    Using two lines for free and reset.
Solution:   Use VIM_CLEAR() instead. (Yegappan Lakshmanan)

src/misc2.c

@@ -4356,10 +4356,7 @@ build_argv_from_list(list_T *l, char ***argv, int *argc)
 	    int i;
 
 	    for (i = 0; i < *argc; ++i)
-	    {
-		vim_free((*argv)[i]);
-		(*argv)[i] = NULL;
-	    }
+		VIM_CLEAR((*argv)[i]);
 	    return FAIL;
 	}
 	(*argv)[*argc] = (char *)vim_strsave(s);