Make Copy-Item to throw exception if source does not exist

Copy-Item command does not throw by default. Thus, copying error is
not caught and the Download function returns without downloading from
the official site. Adding "-errorAction stop" makes Copy-Item to throw
an exception as expected in the script.

Change-Id: I889cccac775705613e641453aca9e0197645f344
Reviewed-by: Simo Fält <simo.falt@qt.io>
Reviewed-by: Toni Saario <toni.saario@qt.io>

coin/provisioning/common/windows/helpers.ps1

@@ -148,7 +148,7 @@ function Download
         if ($CachedUrl.StartsWith("http")) {
             Invoke-WebRequest -UseBasicParsing $CachedUrl -OutFile $Destination
         } else {
-            Copy-Item $CachedUrl $Destination
+            Copy-Item $CachedUrl $Destination -errorAction stop
         }
     } catch {
         Write-Host "Cached download failed: Downloading from official location: $OfficialUrl"