UI: Ensure OBS launches when theme is missing

This change makes it so OBS will still launch even if a theme is
missing. This change also deprecates the "CurrentTheme" config key, and
is replaced by "CurrentTheme2".

This is because a previous change to make sure OBS fell back to the
System theme in case of a missing theme had been accidentally removed.
Changing the key prevents a new version of OBS setting a theme that
doesn't exist in an older version, which would prevent that version from
launching.

UI/obs-app.cpp

@@ -1059,21 +1059,27 @@ bool OBSApp::InitTheme()
 	defaultPalette = palette();
 
 	const char *themeName =
-		config_get_string(globalConfig, "General", "CurrentTheme");
+		config_get_string(globalConfig, "General", "CurrentTheme2");
 
-	if (!themeName) {
+	if (!themeName)
+		/* Use deprecated "CurrentTheme" value if available */
+		themeName = config_get_string(globalConfig, "General",
+					      "CurrentTheme");
+	if (!themeName)
 		/* Use deprecated "Theme" value if available */
 		themeName = config_get_string(globalConfig, "General", "Theme");
-		if (!themeName)
-			themeName = DEFAULT_THEME;
-		if (!themeName)
-			themeName = "Dark";
-	}
+	if (!themeName)
+		themeName = DEFAULT_THEME;
+	if (!themeName)
+		themeName = "Dark";
 
 	if (strcmp(themeName, "Default") == 0)
 		themeName = "System";
 
-	return SetTheme(themeName);
+	if (strcmp(themeName, "System") != 0 && SetTheme(themeName))
+		return true;
+
+	return SetTheme("System");
 }
 
 OBSApp::OBSApp(int &argc, char **argv, profiler_name_store_t *store)

UI/window-basic-settings.cpp

@@ -2726,7 +2726,7 @@ void OBSBasicSettings::SaveGeneralSettings()
 		themeData = DEFAULT_THEME;
 
 	if (WidgetChanged(ui->theme)) {
-		config_set_string(GetGlobalConfig(), "General", "CurrentTheme",
+		config_set_string(GetGlobalConfig(), "General", "CurrentTheme2",
 				  QT_TO_UTF8(themeData));
 
 		App()->SetTheme(themeData.toUtf8().constData());