Trying to open a file for which the user does not have read permission throws with non-helpful message

[SugoiDev]

Using JustAssembly 2018.1.323.2 on win10 x64, if you paste the path of a file the user doesn't have read permissions, the following exception will be thrown

Object reference not set to an instance of an object.
   at Mono.Cecil.Extensions.ModuleDefinitionExtensions.BuildNamespaceHierarchyTree(AssemblyDefinition self) in c:\Jenkins\ReleaseFullWithUploadBuild\workspace\JustDecompileEngine\Cecil.Decompiler\Mono.Cecil.Extensions\ModuleDefinitionExtensions.cs:line 16
   at JustDecompile.Tools.MSBuildProjectBuilder.BaseProjectBuilder..ctor(String assemblyPath, String targetPath, ILanguage language, IFrameworkResolver frameworkResolver, IDecompilationPreferences preferences, IFileGenerationNotifier notifier, IAssemblyInfoService assemblyInfoService, VisualStudioVersion visualStudioVersion, ProjectGenerationSettings projectGenerationSettings, IProjectGenerationNotifier projectNotifier) in c:\Jenkins\ReleaseFullWithUploadBuild\workspace\JustDecompileEngine\MSBuildProjectCreator\BaseProjectBuilder.cs:line 150
   at JustDecompile.External.JustAssembly.JustAssemblyProjectBuilder..ctor(String assemblyPath, String targetPath, ILanguage language, IFileGenerationNotifier notifier) in c:\Jenkins\ReleaseFullWithUploadBuild\workspace\JustDecompileEngine\JustDecompile.External.JustAssembly\JustAssemblyProjectBuilder.cs:line 23
   at JustDecompile.External.JustAssembly.Decompiler.GenerateFiles(String assemblyFilePath, String targetPath, SupportedLanguage language, CancellationToken cancellationToken, IFileGenerationNotifier notifier) in c:\Jenkins\ReleaseFullWithUploadBuild\workspace\JustDecompileEngine\JustDecompile.External.JustAssembly\Decompiler.cs:line 319
   at JustAssembly.Nodes.AssemblyNode.<>c__DisplayClass6.<LoadItemsAsync>b__3() in c:\Jenkins\ReleaseFullWithUploadBuild\workspace\UI\JustAssembly\Nodes\AssemblyNode.cs:line 151

Continuing, the following message will be shown (not very helpful): Not supported file(s):, and a file list will be shown.

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I think the security exception should be shown to to the user instead.