fix bug

Author: michael xu

finplotWindow.py

@@ -390,10 +390,10 @@ def _date_str2x(self, ax, date_str):
         print(date_str)
 
         if ax.getAxis('bottom').vb.datasrc is None:
-
             df = self.last_ax_data_xtick
         else:
             df = ax.getAxis('bottom').vb.datasrc.df
+            self.last_ax_data_xtick = df
 
         dftime = np.array(df.iloc[:, 0])
         lsttime = dftime.tolist()