VsTestConsoleWrapper.DiscoverTests throughs exception if VsTestConsoleWrapper.InitializeExtensions is not called with non null parameter

[Faizan2304]

Exception:

Parameter name: o
   at Newtonsoft.Json.Linq.JToken.FromObjectInternal(Object o, JsonSerializer jsonSerializer)
   at Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.JsonDataSerializer.SerializePayload(String messageType, Object payload, Int32 version)
   at Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.SocketCommunicationManager.SendMessage(String messageType, Object payload, Int32 version)
   at Microsoft.TestPlatform.VsTestConsole.TranslationLayer.VsTestConsoleRequestSender.InitializeExtensions(IEnumerable 1 pathToAdditionalExtensions)
   at Microsoft.TestPlatform.VsTestConsole.TranslationLayer.VsTestConsoleWrapper.EnsureInitialized()
   at Microsoft.TestPlatform.VsTestConsole.TranslationLayer.VsTestConsoleWrapper.DiscoverTests(IEnumerable`1 sources, String discoverySettings, ITestDiscoveryEventsHandler discoveryEventsHandler)

Root cause

When we don't initialize VsTestConsoleWrapper.pathToAdditionalExtensions with non null value the default value of VsTestConsoleWrapper.pathToAdditionalExtensions become null and hence serialization function through exception.

Fix

initialize VsTestConsoleWrapper.pathToAdditionalExtensions in constructor with empty list.