Fix Practice Rate changing causing Player Options to reset rate to 0.5x

floating point errors and stuff cause tiny errors that, when the game tries to match those to existing player option strings, reveal errors
... so basically 1.05 is more like 1.049999995 and thats not good

src/Etterna/Screen/Gameplay/ScreenGameplayPractice.cpp

@@ -426,7 +426,7 @@ float
 ScreenGameplayPractice::AddToRate(float amountAdded)
 {
 	float rate = GAMESTATE->m_SongOptions.GetCurrent().m_fMusicRate;
-	float newRate = rate + amountAdded;
+	double newRate = std::floor((rate + amountAdded) * 100 + 0.5) / 100;
 
 	// Rates outside of this range may crash
 	// Use 0.25 because of floating point errors...