Simplify lpf filter code

Begin with zero instead of the initializing value, as the latter doesn't make much sense in practice, but complicates the code much.

flix/lpf.h

@@ -14,15 +14,6 @@ public:
 	LowPassFilter(float alpha): alpha(alpha) {};
 
 	T update(const T input) {
-		if (alpha == 1) { // filter disabled
-			return input;
-		}
-
-		if (!initialized) {
-			output = input;
-			initialized = true;
-		}
-
 		return output += alpha * (input - output);
 	}
 
@@ -31,9 +22,6 @@ public:
 	}
 
 	void reset() {
-		initialized = false;
+		output = T(); // set to zero
 	}
-
-private:
-	bool initialized = false;
 };