Fix multiple instance bug

src/Core/Platform/PlatformWin.cpp

@@ -324,6 +324,24 @@ namespace Core::Platform {
 	}
 
 	bool isOtherInstanceRunning(int argc, char** argv){
+		// We create a system-wide mutex with a unique name. If it does not exist, we know
+		// there are no other instances. This is a fix for an issue where some windows had
+		// a title of "Etterna" and it generated false positives (Notably explorer on an Etterna folder)
+		//
+		// SHA256 of ETTERNA in the middle
+		CreateMutex(NULL, TRUE, TEXT(" ETTERNA2aced23fdf1270d6a97c9425f957829fce5ad666fec0c6fdfcdae5561f8b905dETTERNA "));
+		switch (GetLastError()) {
+			case ERROR_SUCCESS:
+				// Process was not running already
+				// We leak the mutex, it is released when our process dies. If another instance
+				// attempts to start it will now fail here.
+				return false;
+			case ERROR_ALREADY_EXISTS:
+				// Process is running already
+			default:
+				// Error occured, not sure whether process is running already.
+				break;
+		}
         /* Search for the existing window.  Prefer to use the class name, which is
          * less likely to have a false match, and will match the gameplay window.
          * If that fails, try the window name, which should match the loading