Add failing test for incorrect start time of storyboard elements

osu.Game.Tests/Beatmaps/Formats/LegacyStoryboardDecoderTest.cs

@@ -117,6 +117,23 @@ namespace osu.Game.Tests.Beatmaps.Formats
             }
         }
 
+        [Test]
+        public void TestEarliestStartTimeWithLoopAlphas()
+        {
+            var decoder = new LegacyStoryboardDecoder();
+
+            using (var resStream = TestResources.OpenResource("loop-containing-earlier-non-zero-fade.osb"))
+            using (var stream = new LineBufferedReader(resStream))
+            {
+                var storyboard = decoder.Decode(stream);
+
+                StoryboardLayer background = storyboard.Layers.Single(l => l.Depth == 3);
+                Assert.AreEqual(1, background.Elements.Count);
+                Assert.AreEqual(1000, background.Elements[0].StartTime);
+                Assert.AreEqual(1000, storyboard.EarliestEventTime);
+            }
+        }
+
         [Test]
         public void TestDecodeVariableWithSuffix()
         {

osu.Game.Tests/Resources/loop-containing-earlier-non-zero-fade.osb

@@ -0,0 +1,8 @@
+osu file format v14
+
+[Events]
+//Storyboard Layer 0 (Background)
+Sprite,Background,TopCentre,"img.jpg",320,240
+ L,1000,1
+  F,0,0,,1       // fade inside a loop with non-zero alpha and an earlier start time should be the true start time..
+ F,0,2000,,0     // ..not a zero alpha fade with a later start time