Fix unchecked malloc()

Found using Infer.
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 709f230..41722e8 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -3066,6 +3066,11 @@
     ssl->min_minor_ver = SSL_MINOR_VERSION_0;
 
     ssl->ciphersuites = malloc( sizeof(int *) * 4 );
+    if( ssl->ciphersuites == NULL )
+    {
+        SSL_DEBUG_MSG( 1, ( "malloc(%d bytes) failed", sizeof(int *) * 4) );
+        return( POLARSSL_ERR_SSL_MALLOC_FAILED );
+    }
     ssl_set_ciphersuites( ssl, ssl_default_ciphersuites );
 
 #if defined(POLARSSL_DHM_C)