FIX: make sure nbagg figure are shown when created

Removing the `draw_if_interactive` from `pyplot.figure` in
b2fbae7 causes the figures to no longer
be shown on creation in nbagg, this special-cases the manager creating
in nbagg to ensure that the figure is indeed shown.

The root cause of this is that unlike every other backend which call
`show` in either the Manager `__init__` or one of the
`new_figure_manager` functions, nbagg did not

Author: tacaswell

lib/matplotlib/backends/backend_nbagg.py

@@ -224,6 +224,9 @@ def new_figure_manager_given_figure(num, figure):
     if rcParams['nbagg.transparent']:
         figure.patch.set_alpha(0)
     manager = FigureManagerNbAgg(canvas, num)
+    if is_interactive():
+        manager.show()
+        figure.canvas.draw_idle()
     return manager