The first author was partly supported by National Natural Science Foundation of China (Grant No. 12071116), the Key Projects of Hunan Provincial Department of Education (Grant No. 21A0429), the Discipline Special Research Projects of Hengyang Normal University (Grant No. XKZX21002), the Science and Technology Plan Project of Hunan Province (Grant No. 2016TP1020), and the Application-Oriented Characterized Disciplines, Double First-Class University Project of Hunan Province (Xiangjiaotong [2018]469). The work of the second author was supported by Mathematical Research Impact Centric Support (MATRICS) of the Department of Science and Technology (DST), India (MTR/2017/000367). Acknowledgements