Do some fix for UnpooledUnsafeDirectByteBuffer

1. Fix the possible data mismatch and `AccessViolationException` for `UnpooledUnsafeDirectByteBuffer` in netcoreapp1.x and some early versions of net472 and netcoreapp2.0
>Apply workaround of dotnet/coreclr#17071 for netcoreapp1.x and some early versions of net472 and netcoreapp2.0
>See the issue at Azure/azure-iot-sdk-csharp#604. DotNetty `0.6.0` already prefer safe version of buffers, but it's also ok to fix it.
>https://gist.github.com/yyjdelete/210da6dfb09a0d588b567e5deada6847 , and try with `dotnet run -c Release -f netcoreapp1.1`

2. Fix the `IndexOutOfRangeException` of `UnpooledUnsafeDirectByteBuffer`
>#415, And when try to read 0 bytes at the end of the buffer(or capacity of buffer is zero).
>Possible also for , and `GetPinnableMemoryAddress()

Will do this when I'm free.