Fixed some of Rider's complaints

src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs

@@ -180,7 +180,7 @@ namespace Avalonia.Utilities
                 {
                     var r = _data[c];
                     if (r?.TryGetTarget(out var sub) == true)
-                        sub.OnEvent(sender, eventArgs);
+                        sub!.OnEvent(sender, eventArgs);
                     else
                         needCompact = true;
                 }

src/Avalonia.Visuals/Media/TextFormatting/Unicode/LineBreakEnumerator.cs

@@ -80,12 +80,12 @@ namespace Avalonia.Media.TextFormatting.Unicode
                     }
                 }
 
-                var shouldBreak = GetSimpleBreak() ?? (bool?)GetPairTableBreak(lastClass);
+                var shouldBreak = GetSimpleBreak() ?? GetPairTableBreak(lastClass);
 
                 // Rule LB8a
                 _lb8a = _nextClass == LineBreakClass.ZWJ;
 
-                if (shouldBreak.Value)
+                if (shouldBreak)
                 {
                     Current = new LineBreak(FindPriorNonWhitespace(_lastPosition), _lastPosition);
                     return true;