Fix short circuit on tw_mount_system_ro

Before mounting /system to check if supersu should be installed (a
feature which really needs to be stripped from TWRP), check if
tw_mount_system_ro is set to zero, not the other way around.

Change-Id: I38386b4c88fab112de5b6b752ecd4eed308efa5a
diff --git a/twrp.cpp b/twrp.cpp
index ff7d55f..d49ae80 100644
--- a/twrp.cpp
+++ b/twrp.cpp
@@ -375,7 +375,7 @@
 	// Disable flashing of stock recovery
 	TWFunc::Disable_Stock_Recovery_Replace();
 	// Check for su to see if the device is rooted or not
-	if (PartitionManager.Mount_By_Path("/system", false) && DataManager::GetIntValue("tw_mount_system_ro") == 0) {
+	if (DataManager::GetIntValue("tw_mount_system_ro") == 0 && PartitionManager.Mount_By_Path("/system", false)) {
 		if (TWFunc::Path_Exists("/supersu/su") && TWFunc::Path_Exists("/system/bin") && !TWFunc::Path_Exists("/system/bin/su") && !TWFunc::Path_Exists("/system/xbin/su") && !TWFunc::Path_Exists("/system/bin/.ext/.su")) {
 			// Device doesn't have su installed
 			DataManager::SetValue("tw_busy", 1);