[plot] The lines displayed by the crossair option blinking a lot
Sometimes it is displayed, sometimes not depending on the mouse location.

As result sometimes the mouse stop and there is no crossair anymore.
diff --git a/silx/gui/plot/backends/BackendMatplotlib.py b/silx/gui/plot/backends/BackendMatplotlib.py
index 1b9fdea0b..233649431 100755
--- a/silx/gui/plot/backends/BackendMatplotlib.py
+++ b/silx/gui/plot/backends/BackendMatplotlib.py
@@ -1266,7 +1266,7 @@ class BackendMatplotlibQt(FigureCanvasQTAgg, BackendMatplotlib):
     def _onMouseMove(self, event):
         if self._graphCursor:
             lineh, linev = self._graphCursor
-            if event.inaxes != self.ax and lineh.get_visible():
+            if event.inaxes not in (self.ax, self.ax2) and lineh.get_visible():
                 lineh.set_visible(False)
                 linev.set_visible(False)
                 self._plot._setDirtyPlot(overlayOnly=True)
['silx/gui/plot/backends/BackendMatplotlib.py']