Minor optimizations (original by Peter Vaskovic, modified by Paul Bakker)

Move strlen out of for loop.
Remove redundant null checks before free.
diff --git a/library/ssl_cache.c b/library/ssl_cache.c
index 9e49b9a..836b685 100644
--- a/library/ssl_cache.c
+++ b/library/ssl_cache.c
@@ -321,8 +321,7 @@
         ssl_session_free( &prv->session );
 
 #if defined(POLARSSL_X509_CRT_PARSE_C)
-        if( prv->peer_cert.p != NULL )
-            polarssl_free( prv->peer_cert.p );
+        polarssl_free( prv->peer_cert.p );
 #endif /* POLARSSL_X509_CRT_PARSE_C */
 
         polarssl_free( prv );