installer: Upgrading to latest preview SDK from previous preview version results in missing ASP.NET Core ref pack

Just experienced this on my desktop. Apparently @davidfowl experience this too on his laptop last week.

1. Started with SDK version 3.0.100-preview7-012606 (Windows x64)
2. Upgraded to version 3.0.100-preview7-012629 (Windows x64)
3. After upgrade, ASP.NET Core projects fail to build with following restore error:

   ~\MyProject.csproj : error NU1102: Unable to find package Microsoft.AspNetCore.App.Ref with version (= 3.0.0-preview7.19325.7)
   ~\MyProject.csproj : error NU1102:   - Found 4 version(s) in nuget.org [ Nearest version: 3.0.0-preview6.19307.2 ]
   ~\MyProject.csproj : error NU1102:   - Found 0 version(s) in Microsoft Visual Studio Offline Packages
   

The contents of C:\Program Files\dotnet\packs is missing the ASP.NET Core ref pack:

Intsaller logs: Microsoft_.NET_Core_SDK_3.0.100_-preview7(x64)_install_logs.zip