Fix platform settings returning empty color

src/iOS/Avalonia.iOS/PlatformSettings.cs

@@ -31,24 +31,25 @@ internal class PlatformSettings : DefaultPlatformSettings
         if (tintColor is not null)
         {
             tintColor.GetRGBA(out var red, out var green, out var blue, out var alpha);
-            return _lastColorValues = new PlatformColorValues
+            if (red != 0 && green != 0 && blue != 0 && alpha != 0)
             {
-                ThemeVariant = themeVariant,
-                ContrastPreference = contrastPreference,
-                AccentColor1 = new Color(
-                    (byte)(alpha * 255),
-                    (byte)(red * 255),
-                    (byte)(green * 255),
-                    (byte)(blue * 255))
-            };
+                return _lastColorValues = new PlatformColorValues
+                {
+                    ThemeVariant = themeVariant,
+                    ContrastPreference = contrastPreference,
+                    AccentColor1 = new Color(
+                        (byte)(alpha * 255),
+                        (byte)(red * 255),
+                        (byte)(green * 255),
+                        (byte)(blue * 255))
+                };
+            }
         }
-        else
+
+        return _lastColorValues = new PlatformColorValues
         {
-            return _lastColorValues = new PlatformColorValues
-            {
-                ThemeVariant = themeVariant, ContrastPreference = contrastPreference
-            };
-        }
+            ThemeVariant = themeVariant, ContrastPreference = contrastPreference
+        };
     }
 
     public void TraitCollectionDidChange()