fix(MarkableTimeBar): align segments to timebar

Due to a error in the timebar position calculation, segments could
be msialigned by a pixel. This is fixed by using a caculation that more
closely matches how the actual timebar is drawn.

app/src/main/java/com/github/libretube/ui/views/MarkableTimeBar.kt

@@ -38,7 +38,7 @@ class MarkableTimeBar(
         canvas.save()
         val horizontalOffset = (parent as View).marginLeft
         length = canvas.width - horizontalOffset * 2
-        val marginY = canvas.height / 2 - progressBarHeight / 2
+        val marginY =  (canvas.height - progressBarHeight) / 2
         val themeColor = ThemeHelper.getThemeColor(context, R.attr.colorOnSecondary)
 
         segments.forEach {
@@ -49,7 +49,7 @@ class MarkableTimeBar(
                     start.toLength() + horizontalOffset,
                     marginY,
                     end.toLength() + horizontalOffset,
-                    canvas.height - marginY
+                    marginY + progressBarHeight
                 ),
                 Paint().apply {
                     color = if (PreferenceHelper.getBoolean("sb_enable_custom_colors", false)) {