Fix Windows unit tests (#5161)

Fixes order of commands in unittests.ps1: inv rtloader.test needs the dependencies provided by inv deps.
Exits early if any of the commands fail.

tasks/winbuildscripts/unittests.ps1

@@ -15,6 +15,8 @@ if ($Env:TARGET_ARCH -eq "x86") {
     $archflag = "x86"
 }
 & go get gopkg.in/yaml.v2
+& inv -e deps --verbose --dep-vendor-only
+
 & inv -e rtloader.make --python-runtimes="$Env:PY_RUNTIMES" --install-prefix=$Env:BUILD_ROOT\dev --cmake-options='-G \"Unix Makefiles\"' --arch $archflag
 $err = $LASTEXITCODE
 Write-Host Build result is $err
@@ -24,6 +26,12 @@ if($err -ne 0){
 }
 
 & inv -e rtloader.install
+$err = $LASTEXITCODE
+Write-Host rtloader install result is $err
+if($err -ne 0){
+    Write-Host -ForegroundColor Red "rtloader install failed $err"
+    [Environment]::Exit($err)
+}
 
 # & inv -e rtloader.format --raise-if-changed
 # $err = $LASTEXITCODE
@@ -35,11 +43,16 @@ if($err -ne 0){
 # }
 
 & inv -e rtloader.test
-& inv -e deps --dep-vendor-only
+$err = $LASTEXITCODE
+Write-Host rtloader test result is $err
+if($err -ne 0){
+    Write-Host -ForegroundColor Red "rtloader test failed $err"
+    [Environment]::Exit($err)
+}
+
 & inv -e test --race --profile --cpus 4 --arch $archflag --python-runtimes="$Env:PY_RUNTIMES" --python-home-2=$Env:Python2_ROOT_DIR --python-home-3=$Env:Python3_ROOT_DIR --rtloader-root=$Env:BUILD_ROOT\rtloader
 $err = $LASTEXITCODE
 Write-Host Test result is $err
-
 if($err -ne 0){
     Write-Host -ForegroundColor Red "test failed $err"
     [Environment]::Exit($err)