GH-1997 fix off by one error in 8.3 path logic

api/logic/minecraft/launch/LauncherPartLaunch.cpp

@@ -36,8 +36,13 @@ QString shortPathName(const QString & file)
 	auto input = file.toStdWString();
 	std::wstring output;
 	long length = GetShortPathNameW(input.c_str(), NULL, 0);
+	// NOTE: this resizing might seem weird...
+	// when GetShortPathNameW fails, it returns length including null character
+	// when it succeeds, it returns length excluding null character
+	// See: https://msdn.microsoft.com/en-us/library/windows/desktop/aa364989(v=vs.85).aspx
 	output.resize(length);
 	GetShortPathNameW(input.c_str(),(LPWSTR)output.c_str(),length);
+	output.resize(length-1);
 	QString ret = QString::fromStdWString(output);
 	return ret;
 }