Error when clicking the refresh button after animation

[Chilipp]

Problem description

When making an animation and clicking the refresh button, one gets the following error (see Screencast below)

Traceback (most recent call last):
File "/home/psommer/Documents/code/development/psyplot/psy-view/psy_view/ds_widget.py", line 333, in reload
num = next(num for num, f in sp.dsnames_map.items() if f == fname)
StopIteration

https://user-images.githubusercontent.com/9960249/116358737-41a81b80-a7fe-11eb-8487-5993080e97e3.mp4

Output of psyplot -aV

``` psy_maps.plugin: requirements: cartopy: 0.18.0 version: 1.3.2+2.g26b6411.dirty psy_reg.plugin: requirements: scipy: 1.5.3 statsmodels: 0.12.2 version: 1.3.0+3.gc849e50 psy_simple.plugin: version: 1.3.1 psy_strat.plugin: version: 0.1.0 psy_transect.plugin: version: 0.0.1.dev0 psyplot: requirements: matplotlib: 3.4.1 numpy: 1.20.2 pandas: 1.2.3 python: 3.8.6 | packaged by conda-forge | (default, Oct 7 2020, 19:08:05) [GCC 7.5.0] xarray: 0.17.0 version: 1.3.1 psyplot_gui: requirements: pyqt: 5.12.3 qt: 5.12.9 qtconsole: 5.0.3 version: 1.3.0

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