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>

demos/state_machine/state_machine.c

@@ -114,7 +114,7 @@ void SSLStateMachine_print_error(SSLStateMachine * pMachine,
 SSLStateMachine *SSLStateMachine_new(const char *szCertificateFile,
                                      const char *szKeyFile)
 {
-    SSLStateMachine *pMachine = malloc(sizeof *pMachine);
+    SSLStateMachine *pMachine = malloc(sizeof(*pMachine));
     int n;
 
     die_unless(pMachine);