Improve max brightness handling

If we can detect the directory, why don't we detect maximum as well?

Additional patch by: Matt Mower
Replace clunky /nobrightness handling

Cleanup TWFunc::Set_Brightness() and blanktimer::getBrightness() a
bit, primarily for the purpose of relying on the value in
tw_has_brightnesss_file instead of checking for a phony brightness
path.

Change-Id: Ib22595df53cefa8db7a1172a581984c42ad461c6
diff --git a/twrp-functions.cpp b/twrp-functions.cpp
index e73a52d..63ed0a6 100644
--- a/twrp-functions.cpp
+++ b/twrp-functions.cpp
@@ -981,20 +981,19 @@
 
 int TWFunc::Set_Brightness(std::string brightness_value)
 {
+	int result = -1;
+	std::string secondary_brightness_file;
 
-	std::string brightness_file = DataManager::GetStrValue("tw_brightness_file");;
-
-	if (brightness_file.compare("/nobrightness") != 0) {
-		std::string secondary_brightness_file = DataManager::GetStrValue("tw_secondary_brightness_file");
+	if (DataManager::GetIntValue("tw_has_brightnesss_file")) {
 		LOGINFO("TWFunc::Set_Brightness: Setting brightness control to %s\n", brightness_value.c_str());
-		int result = TWFunc::write_file(brightness_file, brightness_value);
-		if (secondary_brightness_file != "") {
-			LOGINFO("TWFunc::Set_Brightness: Setting SECONDARY brightness control to %s\n", brightness_value.c_str());
+		result = TWFunc::write_file(DataManager::GetStrValue("tw_brightness_file"), brightness_value);
+		DataManager::GetValue("tw_secondary_brightness_file", secondary_brightness_file);
+		if (!secondary_brightness_file.empty()) {
+			LOGINFO("TWFunc::Set_Brightness: Setting secondary brightness control to %s\n", brightness_value.c_str());
 			TWFunc::write_file(secondary_brightness_file, brightness_value);
 		}
-		return result;
 	}
-	return -1;
+	return result;
 }
 
 bool TWFunc::Toggle_MTP(bool enable) {