Always call Unlock

Please note that you always have to call Unlock, even when TryLock fails, as can be seen from the reference source implementation https://referencesource.microsoft.com/#PresentationCore/Core/CSharp/System/Windows/Interop/D3DImage.cs

The internal reference count is incremented, even when TryLock fails. This is rather counter-intuitive IMHO.

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* ID: fed3b5af-09ad-a98f-07a8-cc439a1f8c3c
* Version Independent ID: 919f14d0-40ee-ef18-44f8-fe138852cb5d
* Content: [D3DImage.TryLock(Duration) Method (System.Windows.Interop)](https://docs.microsoft.com/en-us/dotnet/api/system.windows.interop.d3dimage.trylock?view=netframework-4.7.2)
* Content Source: [xml/System.Windows.Interop/D3DImage.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Windows.Interop/D3DImage.xml)
* Product: **dotnet-api**
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* Microsoft Alias: **dotnetcontent**