Don't try to show xhair if no active plot

piker/ui/_chart.py

@@ -172,6 +172,7 @@ class ChartSpace(QtGui.QWidget):
 
             # XXX: pretty sure we don't need this
             # remove any existing plots?
+            # XXX: ahh we might want to support cache unloading..
             # self.vbox.removeWidget(self.linkedcharts)
 
         # switching to a new viewable chart

piker/ui/_graphics/_cursor.py

@@ -435,7 +435,12 @@ class Cursor(pg.GraphicsObject):
         self,
         y_label_level: float = None,
     ) -> None:
-        g = self.graphics[self.active_plot]
+
+        plot = self.active_plot
+        if not plot:
+            return
+
+        g = self.graphics[plot]
         # show horiz line and y-label
         g['hl'].show()
         g['vl'].show()