Update package.ps1 (#996)

* Update package.ps1

* Update eng/package.ps1

Co-authored-by: Javier Suárez <javiersuarezruiz@hotmail.com>

Co-authored-by: Rui Marinho <me@ruimarinho.net>
Co-authored-by: Javier Suárez <javiersuarezruiz@hotmail.com>

eng/package.ps1

@@ -58,6 +58,7 @@ if ($IsWindows)
             /t:build `
             /p:Packing=true `
             /bl:"$artifacts/maui-build-$configuration.binlog"
+        if (!$?) { throw "Build failed." }
 
         & $msbuild $sln `
             /p:configuration=$configuration `
@@ -65,6 +66,7 @@ if ($IsWindows)
             /t:pack `
             /p:Packing=true `
             /bl:"$artifacts/maui-pack-$configuration.binlog"
+        if (!$?) { throw "Pack failed." }
     }
     finally
     {
@@ -86,4 +88,5 @@ else
         -c:$configuration `
         -p:SymbolPackageFormat=snupkg `
         -bl:$artifacts/maui-pack-$configuration.binlog
+    if (!$?) { throw "Pack failed." }
 }