Delete underlying ssecurity in SSecurityVeNCrypt.

Otherwise it gets leaked which would allow even not authenticated clients to exhaust server memory.
diff --git a/common/rfb/SSecurityVeNCrypt.cxx b/common/rfb/SSecurityVeNCrypt.cxx
index 7c13749..ce6c71b 100644
--- a/common/rfb/SSecurityVeNCrypt.cxx
+++ b/common/rfb/SSecurityVeNCrypt.cxx
@@ -55,6 +55,8 @@
 
 SSecurityVeNCrypt::~SSecurityVeNCrypt()
 {
+  delete ssecurity;
+
   if (subTypes) {
     delete [] subTypes;
     subTypes = NULL;