plotting_widget.py fix bug when zooming inside gap where there's no data

sohstationviewer/view/plotting/plotting_widget/plotting_widget.py

@@ -575,6 +575,8 @@ class PlottingWidget(QtWidgets.QScrollArea):
                     tr_min_ys = []
                     tr_max_ys = []
                     for x, y in zip(ax.x_list, ax.y_list):
+                        if len(x) == 0:
+                            continue
                         if self.min_x > x[-1] or self.max_x < x[0]:
                             continue
                         ret = get_total_miny_maxy(x, y, self.min_x, self.max_x)