LibPathResolver::GetSearchLocations returning null causing exception to be thrown

[argfoo-web3]

As it is possible for Assembly.GetEntryAssembly to return null in LibPathResolver::GetSearchLocations, null checking has to be done.

Code should add null handling here from:

yield return Path.GetDirectoryName(Assembly.GetEntryAssembly().Location);

to:

var entryAssembly = Assembly.GetEntryAssembly();
if(entryAssembly != null)
{
yield return Path.GetDirectoryName(entryAssembly.Location);
}