Fixes to AvoidNullOrEmptyHelpMessageAttribute.
Fixes to AvoidNullOrEmptyHelpMessageAttribute.

Instead of using ast.extent property for comparing empty string or null argument we use the parsed values.

daviwil/PSScriptAnalyzer,PowerShell/PSScriptAnalyzer,juneb/PSScriptAnalyzer,dlwyatt/PSScriptAnalyzer,rkeithhill/PSScriptAnalyzer