Fix check settings for CLion and Mono

[shiena]

Invalid value is set for CLion executable and CLion execution fails. I fixed to prevent steps 8 and 10 below.

To reproduction

1. Open the CLion settings in Project Settings Window
2. Set the path to the CLion executable
3. Open other settings
4. Open CLion settings
5. Remove the path to the CLion executable
6. Open other settings
7. Open CLion settings
8. UE4 folder path is set in the path to the CLion executable (e.g. C:\Program Files\Epic Games\UE_4.17\Engine\Binaries\Win64\ )
   • If CLion.FilePath is empty, the following returns the working directory of UE4 Editor. https://github.com/dotBunny/CLionSourceCodeAccess/blob/24f363a89f966d68b49b7c53c3fc7bf2a6b950ca/Source/CLionSourceCodeAccess/Private/CLionSettings.cpp#L153
9. Select Open CLion from File menu

10. Error in Output Log

    LogWindows: Warning: CreateProc failed (5) C:/Program Files/Epic Games/UE_4.17/Engine/Binaries/Win64/ "C:/Users/shiena/Documents/Unreal Projects/MyProjectCpp/"

    • CLion.FilePath is not checked before running CLion. https://github.com/dotBunny/CLionSourceCodeAccess/blob/4f8b9dc181aab5adf666524624ca77e1555a7d65/Source/CLionSourceCodeAccess/Private/CLionSourceCodeAccessor.cpp#L575-L592