manifest.EntryPoint is null net6

Getting NRE in Command.cs ([line 1640](https://github.com/dotnet/deployment-tools/blob/279aaf0f89c0072052f9f21a818a652109f5ea51/src/clickonce/MageCLI/Command.cs#L1640)) because manifest.EntryPoint is null.

Reproduce the error by building a simple application like this:
```xml

Static


WinExe
net6.0-windows
win10-x64
true
latest
FHCDocumentImportExport.App
true
...
```
Then build it with
```powershell
dotnet build yourproject.csproj /p:Version=1.2.3.4 /p:OutputPath=...
```
Then finally run:
```powershell
deployment-tools\artifacts\bin\MageCLI\Debug\net7.0\dotnet-mage.exe -new Application -t client\FHCDocumentImportExport.manifest -fd client -v 1.2.3.4 -p amd64
```
### Actual result:
Internal error, please try again. Object reference not set to an instance of an object.
### Expected result:
should generate properly the app manifest