Trying to build without CMake installed gives a confusing error message

Namely

.\build.libgit2.ps1 14
Index was outside the bounds of the array.
At C:\source\github.com\libgit2sharp\libgit2sharp.nativebinaries\build.libgit2.ps1:71 char:16
+     $cmake = @(Get-Command cmake.exe)[0] 2>$null
+                ~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: (:) [], IndexOutOfRangeException
    + FullyQualifiedErrorId : System.IndexOutOfRangeException

which seems to come from @(Get-Command cmake.exe) returning an empty array.

從第 71 行的 build.libgit2.ps1 開始，在 cmake.exe 無法使用時重現建置流程。檢查如何處理 Get-Command cmake.exe 的空結果，然後在沒有 CMake 的情況下執行指令碼，以確認它回報的是清楚且可採取行動的錯誤，而不是 IndexOutOfRangeException。