Access Violation on Excel 2010 shutdown with CustomTaskPane

Hi,

Firstly, thanks for ExcelDNA!

I'm having problem with Add-ins **with a CustomTaskPane** when running in Excel 2010 (Version 14.0.4760.1000 (64-bit)). The process always exits with either an Access violation, or exit code -2146234327 as shown in the debug logs below.

```
The program '[5968] EXCEL.EXE' has exited with code -2146234327 (0x80131029).
The program '[5968] EXCEL.EXE: Program Trace' has exited with code 0 (0x0).
```
or
```
The program '[6284] EXCEL.EXE: Program Trace' has exited with code 0 (0x0).
The program '[6284] EXCEL.EXE' has exited with code -1073741819 (0xc0000005) 'Access violation'.
```

This doesn't just happen when running in Visual Studio, I also get the `Microsoft Excel has stopped working` message when opening the XLL directly.

I've tested with both versions 34.6 and 33.9 - both show the same error.

Excel 2013 and 2016 work fine.

[This very simple project](https://github.com/Excel-DNA/ExcelDna/files/1910598/AccessViolationTest.zip) displays the problem.

I appreciate Excel 2010 is an ancient version, but I don't control the version my users run, and this is quite a headache for them. Any ideas how I can prevent this error? Many thanks!