Checks validity of imported extension.

Assets/Cryville/Crtr/Extensions/ExtensionImporter.cs

@@ -1,4 +1,6 @@
 using Cryville.Crtr.Extension;
+using Mono.Cecil;
+using System;
 using System.IO;
 
 namespace Cryville.Crtr.Extensions {
@@ -9,6 +11,14 @@ namespace Cryville.Crtr.Extensions {
 		}
 
 		public override void Convert(FileInfo file, ConversionSession ses) {
+			try {
+				using (var stream = file.OpenRead()) {
+					ModuleDefinition.ReadModule(stream, new ReaderParameters(ReadingMode.Immediate));
+				}
+			}
+			catch (BadImageFormatException ex) {
+				throw new FormatException("Invalid extension.", ex);
+			}
 			ses.AddResource(new ExtensionResource(file.Name, file));
 		}
 	}