fix(plugin): Version.TryParse→try-catch + LoadPngBytes null→throw + FileShare.ReadWrite追加

【Mono非互換】
- Version.TryParse は .NET 4.0+ で Unity 5.6 Mono に存在しない
  → try-catch new Version() に置換 (GuessCompressed, Load)

【ArgumentNullException根本原因】
- LoadPngBytes(BinaryReader) が GetPngSize==0 時に null 返却
  → BinaryWriter.Write(null) で ArgumentNullException
  → null返却を廃止、InvalidOperationException を throw

- LoadPngBytes(string) の FileStream に FileShare.ReadWrite が不足
  → ゲームがファイルを掴んでると読めず GetPngSize==0 に

Author: solidlime

src/Plugin/Extension/ImageHelper.cs

@@ -83,7 +83,7 @@ public static void SkipPng(BinaryReader br)
         public static byte[] LoadPngBytes(string path)
         {
             if (path == null) throw new ArgumentNullException(nameof(path));
-            using (FileStream st = new FileStream(path, FileMode.Open, FileAccess.Read))
+            using (FileStream st = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
                 return LoadPngBytes(st);
         }
 
@@ -98,7 +98,7 @@ public static byte[] LoadPngBytes(BinaryReader br)
         {
             if (br == null) throw new ArgumentNullException(nameof(br));
             long pngSize = GetPngSize(br);
-            if (pngSize == 0) return null;
+            if (pngSize == 0) throw new InvalidOperationException("Failed to read PNG data from stream (invalid or missing PNG signature/chunks).");
             return br.ReadBytes((int)pngSize);
         }
     }

src/Plugin/PngCompression/PngCompression.cs

@@ -177,7 +177,14 @@ public long Load(Stream inputStream, Stream outputStream, string token = null, b
                     switch (token)
                     {
                         case Token.StudioToken:
-                            checkfail = !Version.TryParse(binaryReader.ReadString(), out Version v) || !v.Equals(new Version(101, 0, 0, 0));
+                            try
+                            {
+                                checkfail = !new Version(binaryReader.ReadString()).Equals(new Version(101, 0, 0, 0));
+                            }
+                            catch
+                            {
+                                checkfail = true;
+                            }
                             break;
                         case Token.CoordinateToken:
                         default:
@@ -267,9 +274,15 @@ public bool GuessCompressed(BinaryReader binaryReader)
                     default:
                         binaryReader.BaseStream.Seek(position, SeekOrigin.Begin);
                         string st = binaryReader.ReadString();
-                        if (Version.TryParse(st, out Version version))
+                        try
+                        {
+                            Version version = new Version(st);
                             return version.Major == 101;
-                        return false;
+                        }
+                        catch
+                        {
+                            return false;
+                        }
                 }
             }
             catch