Restore 2.3.1 version check (part 2)

UndertaleModLib/Models/UndertaleAnimationCurve.cs

@@ -133,6 +133,7 @@ public void Unserialize(UndertaleReader reader)
             Name = reader.ReadUndertaleString();
             Function = (FunctionType)reader.ReadUInt32();
             Iterations = reader.ReadUInt32();
+
             Points = reader.ReadUndertaleObject<UndertaleSimpleList<Point>>();
         }
 
@@ -141,6 +142,30 @@ public static uint UnserializeChildObjectCount(UndertaleReader reader)
         {
             reader.Position += 12;
 
+            // This check is partly duplicated from UndertaleChunks.cs, but it's necessary to handle embedded curves
+            // (For example, those in SEQN in the TS!Underswap v1.0 demo; see issue #1414)
+            if (!reader.undertaleData.IsVersionAtLeast(2, 3, 1))
+            {
+                long returnPosition = reader.AbsPosition;
+                uint numPoints = reader.ReadUInt32();
+                if (numPoints > 0)
+                {
+                    reader.AbsPosition += 8;
+                    if (reader.ReadUInt32() != 0) // In 2.3 a int with the value of 0 would be set here,
+                    {                             // it cannot be version 2.3 if this value isn't 0
+                        reader.undertaleData.SetGMS2Version(2, 3, 1);
+                    }
+                    else
+                    {
+                        if (reader.ReadUInt32() == 0)                      // At all points (besides the first one)
+                            reader.undertaleData.SetGMS2Version(2, 3, 1);  // if BezierX0 equals to 0 (the above check)
+                                                                           // then BezierY0 equals to 0 as well (the current check)
+                    }
+                }
+
+                reader.AbsPosition = returnPosition;
+            }
+
             // "Points"
             uint count = reader.ReadUInt32();
             if (reader.undertaleData.IsVersionAtLeast(2, 3, 1))

UndertaleModLib/UndertaleChunks.cs

@@ -1504,6 +1504,8 @@ public class UndertaleChunkACRV : UndertaleListChunk<UndertaleAnimationCurve>
         public override string Name => "ACRV";
 
         private static bool checkedForGMS2_3_1;
+
+        // See also a similar check in UndertaleAnimationCurve.cs, necessary for embedded animation curves.
         private void CheckForGMS2_3_1(UndertaleReader reader)
         {
             if (reader.undertaleData.IsVersionAtLeast(2, 3, 1))
@@ -1522,10 +1524,10 @@ private void CheckForGMS2_3_1(UndertaleReader reader)
                 return;
             }
 
-            reader.AbsPosition = reader.ReadUInt32(); // go to the first "Point"
+            reader.AbsPosition = reader.ReadUInt32(); // Go to the first "Point"
             reader.Position += 8;
 
-            if (reader.ReadUInt32() != 0) // in 2.3 a int with the value of 0 would be set here,
+            if (reader.ReadUInt32() != 0) // In 2.3 a int with the value of 0 would be set here,
             {                             // it cannot be version 2.3 if this value isn't 0
                 reader.undertaleData.SetGMS2Version(2, 3, 1);
             }