tidy up and check for previous install

Install-4KVideoDownloader.ps1

@@ -1,16 +1,18 @@
-
-
-## Specify the URL to download 4K Video Downloader from
+## Specify the URL to download the app from
 $URL = 'https://dl.4kdownload.com/app/4kvideodownloader_4.16.0_x64.msi'
 
-## Install Adobe Connect
-If ( IsURLValid $URL ) {
-    LogMsg "Downloading installer from ${URL}"
+## Make sure the app isn't already installed
+If (! (Test-Path "${Env:ProgramFiles}\4KDownload\4kvideodownloader\4kvideodownloader.exe") ) {
+
+    ## Download the installer
     $INSTALLER = Download-File -URL $URL
+
+    ## Install the app
     Try { Start-Process "msiexec.exe" -ArgumentList "/i ${INSTALLER} /qn /norestart" -Wait }
     Catch { LogErr $_.Exception.Message }
+
+    ## Delete the installer
     LogMsg "Deleting downloaded installer from ""${INSTALLER}"""
     Try { Remove-Item -Path $INSTALLER -Force -ErrorAction SilentlyContinue }
     Catch { LogErr $_.Exception.Message }
 }
-Else { LogMsg "URL is not valid: ${URL}" }