Improve error logging for exec of pscommands

[rkeithhill]

This improves the output to the EditorServices.log file from:

1/4/2018 6:49:26 PM [ERROR] - Method "ExecuteCommand" at line 575 of C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\src\PowerShellEditorServices\Session\PowerShellContext.cs

    Execution completed with errors:

    You cannot call a method on a null-valued expression.
    You cannot call a method on a null-valued expression.

to

1/4/2018 6:49:26 PM [ERROR] - Method "ExecuteCommand" at line 575 of C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\src\PowerShellEditorServices\Session\PowerShellContext.cs

    Execution of command 'Import-Module - C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\bin\Desktop\..\..\Commands\PowerShellEditorServices.Commands.psd1;' completed with errors:
    
    Error #1:
    You cannot call a method on a null-valued expression.
    ScriptStackTrace:
    at Register-EditorCommand<Process>, C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\Commands\Public\CmdletInterface.ps1: line 51
    at <ScriptBlock>, C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\Commands\Private\BuiltInCommands.ps1: line 1
    at <ScriptBlock>, C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\Commands\PowerShellEditorServices.Commands.psm1: line 12
    Exception System.Management.Automation.RuntimeException: You cannot call a method on a null-valued expression.
       at CallSite.Target(Closure , CallSite , Object , Object )
       at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
       at System.Management.Automation.Interpreter.DynamicInstruction`3.Run(InterpretedFrame frame)
       at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
    
    Error #2:
    You cannot call a method on a null-valued expression.
    ScriptStackTrace:
    at Register-EditorCommand<Process>, C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\Commands\Public\CmdletInterface.ps1: line 51
    at <ScriptBlock>, C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\Commands\Private\BuiltInCommands.ps1: line 11
    at <ScriptBlock>, C:\Users\Keith\GitHub\rkeithhill\PowerShellEditorServices\module\PowerShellEditorServices\Commands\PowerShellEditorServices.Commands.psm1: line 12
    Exception System.Management.Automation.RuntimeException: You cannot call a method on a null-valued expression.
       at CallSite.Target(Closure , CallSite , Object , Object )
       at System.Management.Automation.Interpreter.DynamicInstruction`3.Run(InterpretedFrame frame)
       at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)

NOTE: While the two errors above "look" identical they actually arise from different lines of BuiltInCommands.ps1.

[daviwil]

This is really helpful, thanks a bunch!

[daviwil]

Weird, I could have sworn I added code for this in the past.

[rkeithhill]

And there very well could be a better place to put this call. I contemplated clearing the error collection at the beginning of the method, before it runs the PSCommand. But I stuck with only clearing after reporting error message. BTW they weren't getting cleared. I kept seeing the same two import failures ($pseditor null) for every subsequent execution - profile loading, prompt eval, etc.

[daviwil]

Nah, this is the right place to do it. I just couldn't believe I hadn't actually added the code. Probably was in a branch somewhere that never got merged :/