UI: Fix preprocessor directives for platform integrations

The macros `YOUTUBE_ENABLED`, `RESTREAM_ENABLED`, and `TWITCH_ENABLED`
are not defined when the associated features are not enabled.
When the code was originally implemented, there were definitions to set
`0` if the feature is disabled. However a later commit 349372b removes
the definition. Now, the use of `#ifdef` is better than just `#if`.

UI/window-basic-settings-stream.cpp

@@ -16,7 +16,7 @@
 
 #include "ui-config.h"
 
-#if YOUTUBE_ENABLED
+#ifdef YOUTUBE_ENABLED
 #include "youtube-api-wrappers.hpp"
 #endif
 
@@ -458,7 +458,7 @@ static void reset_service_ui_fields(Ui::OBSBasicSettings *ui,
 	ui->disconnectAccount->setVisible(false);
 }
 
-#if YOUTUBE_ENABLED
+#ifdef YOUTUBE_ENABLED
 static void get_yt_ch_title(Ui::OBSBasicSettings *ui)
 {
 	const char *name = config_get_string(OBSBasic::Get()->Config(),
@@ -560,7 +560,7 @@ void OBSBasicSettings::ServiceChanged()
 	auto system_auth_service = main->auth->service();
 	bool service_check = service.find(system_auth_service) !=
 			     std::string::npos;
-#if YOUTUBE_ENABLED
+#ifdef YOUTUBE_ENABLED
 	service_check = service_check ? service_check
 				      : IsYouTubeService(system_auth_service) &&
 						IsYouTubeService(service);
@@ -728,7 +728,7 @@ void OBSBasicSettings::OnOAuthStreamKeyConnected()
 		} else {
 			ui->bandwidthTestEnable->setChecked(false);
 		}
-#if YOUTUBE_ENABLED
+#ifdef YOUTUBE_ENABLED
 		if (IsYouTubeService(a->service())) {
 			ui->key->clear();
 
@@ -983,7 +983,7 @@ void OBSBasicSettings::UpdateServiceRecommendations()
 	}
 #undef ENFORCE_TEXT
 
-#if YOUTUBE_ENABLED
+#ifdef YOUTUBE_ENABLED
 	if (IsYouTubeService(QT_TO_UTF8(ui->service->currentText()))) {
 		if (!text.isEmpty())
 			text += "<br><br>";