[build.ps1] fix wrong path, enable builds only if env variable is present

build.ps1

@@ -16,6 +16,7 @@ if ((Get-Command "cl.exe" -ErrorAction SilentlyContinue) -eq $null)
   Write-Host "Visual Studio 2017 ${vstype} Command Prompt variables set.`n" -ForegroundColor Yellow
 }
 
+if (Test-Path env:VCPKG_ROOT) {
   # DEBUG
   New-Item -Path .\build_win_debug -ItemType directory -Force
   Set-Location build_win_debug
@@ -29,10 +30,14 @@ Set-Location build_win_release
   cmake -G "Visual Studio 15 2017" -T "host=x64" -A "x64" "-DCMAKE_TOOLCHAIN_FILE=$env:VCPKG_ROOT\scripts\buildsystems\vcpkg.cmake" "-DVCPKG_TARGET_TRIPLET=$env:VCPKG_DEFAULT_TRIPLET"   "-DCMAKE_BUILD_TYPE=Release" ..
   cmake --build . --config Release --parallel ${number_of_build_workers}
   Set-Location ..
+}
+else {
+  Write-Host "Skipping vcpkg-enabled builds because the VCPKG_ROOT environment variable is not defined`n" -ForegroundColor Yellow
+}
 
 # USE LOCAL PTHREAD LIB, NO VCPKG: remember to use "vcpkg.exe integrate remove" in case you had enable user-wide vcpkg integration
 New-Item -Path .\build_win_release_cuda_int_libs -ItemType directory -Force
-Set-Location build_win_release_cuda_custom_libs
+Set-Location build_win_release_cuda_int_libs
 cmake -G "Visual Studio 15 2017" -T "host=x64" -A "x64" ..
 cmake --build . --config Release --parallel ${number_of_build_workers}
 Set-Location ..