validate `folly::RequestContext` is provided to when calling `collectRequestDebugLog`
validate `folly::RequestContext` is provided to when calling `collectRequestDebugLog`

Summary: to improve user experience when API is not used correctly

Reviewed By: sethdelliott

Differential Revision: D30648958

fbshipit-source-id: 1b60f4991bc1ac2bff268390dbbd7ed54391f3cb

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift