Cast Unix time to uint in the randomize function

This returns a double while the other values are all uint64_t. The
clang compiler gives a warning since converting the constant to double
loses precision.

core/math/random_pcg.cpp

@@ -39,7 +39,7 @@ RandomPCG::RandomPCG(uint64_t p_seed, uint64_t p_inc) :
 }
 
 void RandomPCG::randomize() {
-	seed((OS::get_singleton()->get_unix_time() + OS::get_singleton()->get_ticks_usec()) * pcg.state + PCG_DEFAULT_INC_64);
+	seed(((uint64_t)OS::get_singleton()->get_unix_time() + OS::get_singleton()->get_ticks_usec()) * pcg.state + PCG_DEFAULT_INC_64);
 }
 
 double RandomPCG::random(double p_from, double p_to) {