Use safer sizeof variant in malloc

For a local variable:
        TYPE *p;
Allocations like this are "risky":
        p = OPENSSL_malloc(sizeof(TYPE));
if the type of p changes, and the malloc call isn't updated, you
could get memory corruption.  Instead do this:
        p = OPENSSL_malloc(sizeof(*p));
Also fixed a few memset() calls that I noticed while doing this.

Reviewed-by: Richard Levitte <levitte@openssl.org>

apps/vms_decc_init.c

@@ -130,7 +130,7 @@ char **copy_argv(int *argc, char *argv[])
      */
 
     int i, count = *argc;
-    char **newargv = app_malloc((count + 1) * sizeof *newargv, "argv copy");
+    char **newargv = app_malloc(sizeof(*newargv) * (count + 1), "argv copy");
 
     for (i = 0; i < count; i++)
         newargv[i] = argv[i];