Fix the find error On OS X, it gives the error:
Fix the find error
On OS X, it gives the error:

```bash
find: ftsopen: No such file or directory
```

and on Ubuntu:

```bash
find: cannot search `': No such file or directory (TaskId:2)
```
(both errors can be verified on CI run before this PR)

This change fixes this error.

mono/msbuild,AndyGerlicher/msbuild,Microsoft/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,mono/msbuild,Microsoft/msbuild,Microsoft/msbuild,Microsoft/msbuild,jeffkl/msbuild,rainersigwald/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,chipitsine/msbuild,mono/msbuild,chipitsine/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,rainersigwald/msbuild,jeffkl/msbuild,chipitsine/msbuild,jeffkl/msbuild,rainersigwald/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,mono/msbuild