Assert that accessCheck isn't called too early

These checks depend on accessRights being set up, this has only happened
if we have done the QUERYING steps.

common/rfb/SConnection.cxx

@@ -23,6 +23,7 @@
 
 #include <stdio.h>
 #include <string.h>
+#include <assert.h>
 #include <rfb/Exception.h>
 #include <rfb/Security.h>
 #include <rfb/clipboardTypes.h>
@@ -346,6 +347,8 @@ void SConnection::setAccessRights(AccessRights ar)
 
 bool SConnection::accessCheck(AccessRights ar) const
 {
+  assert(state_ >= RFBSTATE_QUERYING);
+
   return (accessRights & ar) == ar;
 }