#2295: Avoid using `GetPEFileOrNull` if we can't actually handle a `null` return value

This improves the exception message shown when trying to disassemble a .nupkg as IL.

ILSpy.ReadyToRun/ReadyToRunLanguage.cs

@@ -106,7 +106,7 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 
 		public override ProjectId DecompileAssembly(LoadedAssembly assembly, ITextOutput output, DecompilationOptions options)
 		{
-			PEFile module = assembly.GetPEFileOrNull();
+			PEFile module = assembly.GetPEFileAsync().GetAwaiter().GetResult();
 			ReadyToRunReaderCacheEntry cacheEntry = GetReader(assembly, module);
 			if (cacheEntry.readyToRunReader == null)
 			{

ILSpy/Languages/ILLanguage.cs

@@ -162,7 +162,7 @@ namespace ICSharpCode.ILSpy
 		{
 			output.WriteLine("// " + assembly.FileName);
 			output.WriteLine();
-			var module = assembly.GetPEFileOrNull();
+			var module = assembly.GetPEFileAsync().GetAwaiter().GetResult();
 			var metadata = module.Metadata;
 			var dis = CreateDisassembler(output, options);