Fix toolbar PP change showing +0 instead of 0

[peppy]

Before	After

[bdach]

You can still have green +0 show with this because flooring/truncating thrice separately is not guaranteed to give you consistent results.

Example: User goes from $1357.6$ total pp to $1358.1$ total pp. The value before floored is $1357$, the value after floored is $1358$, but the delta is $1358.1 - 1357.6 = 0.5$ which will get floored to 0. Thus you get a point of pp increase shown but a green +0 on the delta.

Can be crudely tested with

diff --git a/osu.Game.Tests/Visual/Menus/TestSceneToolbarUserButton.cs b/osu.Game.Tests/Visual/Menus/TestSceneToolbarUserButton.cs
index a81c940d82..3d18dc5ebc 100644
--- a/osu.Game.Tests/Visual/Menus/TestSceneToolbarUserButton.cs
+++ b/osu.Game.Tests/Visual/Menus/TestSceneToolbarUserButton.cs
@@ -137,12 +137,12 @@ public void TestTransientUserStatisticsDisplay()
                     new UserStatistics
                     {
                         GlobalRank = 111_111,
-                        PP = 1357
+                        PP = 1357.6m
                     },
                     new UserStatistics
                     {
                         GlobalRank = 111_111,
-                        PP = 1357.1m
+                        PP = 1358.1m
                     });
             });
             AddStep("Was null", () =>

[frenzibyte]

We probably want to do (int)after - (int)before on the second argument.

[peppy]

Probably fine.