[bugfix] Calls to unpredictableSeed() should .popFront() internal RNG.

We can also avoid the necessity for a wrapper struct by initializing
the RNG to null and then checking for null status instead of against
a static boolean variable.
Singleton-esque pattern for thread-local static class inside rndGen.

Instead of wrapping with a struct, we initialize to null and then
can check for seeding by checking for null instead of against a
static boolean.