Normalize volume for brightness

Undo an unintentional change done in f6a429e.
The brightness was calculated from the normalized volume, but when factoring
the norm out in the history, that norm was dropped.

app/src/main/kotlin/de/rochefort/childmonitor/VolumeView.kt

@@ -52,10 +52,11 @@ class VolumeView : View {
         val width = width
         val size = volumeHistory.size() // Size is at most width
         val volumeNorm = volumeHistory.volumeNorm
+        val minBrightness = 0.3
         val relativeBrightness: Double = if (size > 0) {
-            volumeHistory[size - 1].coerceAtLeast(0.3)
+            (volumeNorm * volumeHistory[size - 1]).coerceAtLeast(minBrightness)
         } else {
-            0.3
+            minBrightness
         }
         val blue: Int
         val rest: Int