ninja windows: don't spam reg.exe calls if we can't find DirectX installation
ninja windows: don't spam reg.exe calls if we can't find DirectX installation

R=thakis@chromium.org
BUG=gyp:289

Review URL: https://chromiumcodereview.appspot.com/10837010

csulmone/gyp,csulmone/gyp,csulmone/gyp,csulmone/gyp