Remove exception in Mt19937::generate()

This implementation is shared across all native engines. Thus the same
reasoning as the previous commits applies, except that the User engine does not
use this method. Thus is only applicable to the Secure engine, which is the
only fallible native engine.

Author: TimWolla

ext/random/engine_mt19937.c

@@ -302,7 +302,6 @@ PHP_METHOD(Random_Engine_Mt19937, generate)
 	generated = engine->algo->generate(engine->status);
 	size = engine->status->last_generated_size;
 	if (EG(exception)) {
-		zend_throw_exception(spl_ce_RuntimeException, "Random number generation failed", 0);
 		RETURN_THROWS();
 	}