Allow querying the shader encoding supported by custom shaders

* This is distinct from target shaders in the remote proxy case - custom shaders
  are built locally.

qrenderdoc/Code/CaptureContext.cpp

@@ -820,6 +820,7 @@ void CaptureContext::LoadCaptureThreaded(const QString &captureFile, const QStri
 
     m_APIProps = r->GetAPIProperties();
 
+    m_CustomEncodings = r->GetCustomShaderEncodings();
     m_TargetEncodings = r->GetTargetShaderEncodings();
 
     m_PostloadProgress = 0.2f;