Handle the WSL optional component not being present in Spring Creators Update where wslapi.dll is always present (#26)

DistroLauncher/DistroLauncher.cpp

@@ -198,7 +198,13 @@ int wmain(int argc, wchar_t const *argv[])
 
     // If an error was encountered, print an error message.
     if (FAILED(hr)) {
-        Helpers::PrintErrorMessage(hr);
+        if (hr == HRESULT_FROM_WIN32(ERROR_LINUX_SUBSYSTEM_NOT_PRESENT)) {
+            Helpers::PrintMessage(MSG_MISSING_OPTIONAL_COMPONENT);
+
+        } else {
+            Helpers::PrintErrorMessage(hr);
+        }
+
         if (prompt) {
             Helpers::PromptForInput();
         }

DistroLauncher/WslApiLoader.h

@@ -6,6 +6,11 @@
 #pragma once
 #include <wslapi.h>
 
+// This error definition is present in the Spring Creators Update SDK.
+#ifndef ERROR_LINUX_SUBSYSTEM_NOT_PRESENT
+#define ERROR_LINUX_SUBSYSTEM_NOT_PRESENT 414L
+#endif // !ERROR_LINUX_SUBSYSTEM_NOT_PRESENT
+
 typedef BOOL    (STDAPICALLTYPE* WSL_IS_DISTRIBUTION_REGISTERED)(PCWSTR);
 typedef HRESULT (STDAPICALLTYPE* WSL_REGISTER_DISTRIBUTION)(PCWSTR, PCWSTR);
 typedef HRESULT (STDAPICALLTYPE* WSL_CONFIGURE_DISTRIBUTION)(PCWSTR, ULONG, WSL_DISTRIBUTION_FLAGS);