buildDotnetModule: run tests on projectFile if testProjectFile is unset

pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-check-hook.sh

···
         local -r maxCpuFlag="1"
     fi
 
-    for project in ${testProjectFile[@]-}; do
+    for project in ${testProjectFile[@]-${projectFile[@]}}; do
         env "LD_LIBRARY_PATH=@libraryPath@" \
             dotnet test "$project" \
               -maxcpucount:$maxCpuFlag \