etw: Fix panic when provider creation fails

There is a cleanup function deferred to remove the provider from the global
provider map. However, this function didn't bind the value of provider ahead of
time, so when the provider creation returned with nil for provider, we tried to
cleanup a nil provider, and panicked.

pkg/etw/provider.go

@@ -130,11 +130,11 @@ func NewProviderWithID(name string, id *guid.GUID, callback EnableCallback) (pro
 	})
 
 	provider = providers.newProvider()
-	defer func() {
+	defer func(provider *Provider) {
 		if err != nil {
 			providers.removeProvider(provider)
 		}
-	}()
+	}(provider)
 	provider.ID = id
 	provider.callback = callback