Make sure `StaticWebAssetMakeReferencedAssetOriginalItemSpecAbsolute` for wasm apps is not empty

[ilonatommy]

In https://github.com/dotnet/runtime/blob/main/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.props#L32-L39 add

<StaticWebAssetMakeReferencedAssetOriginalItemSpecAbsolute Condition="'$(StaticWebAssetMakeReferencedAssetOriginalItemSpecAbsolute)' == ''">true</StaticWebAssetMakeReferencedAssetOriginalItemSpecAbsolute>

like we do for https://github.com/dotnet/sdk/blob/7d093038ebba148c3d03c5b223127e490df4b0d5/src/BlazorWasmSdk/Targets/Microsoft.NET.Sdk.BlazorWebAssembly.Current.props#L33.

Fixes: dotnet/aspnetcore#62915