aspect ratio requires draw for cartopy maps

The following leads to a wrong figure size:

```python
f, axs = plt.subplots(2, 1, subplot_kw=dict(projection=ccrs.Robinson()))
f.subplots_adjust(hspace=0, wspace=0, top=1, bottom=0, left=0, right=1)
mpu.set_map_layout(axs, width=17)  # width is in cm
print("Size (w x h):  ", np.round(f.get_size_inches() * 2.54, 2))
```

cartopy maps seem to require a `f.canvas.draw()` command


