error raised by prop cycler will still add call to axes

[kecnry]

... but not all paperwork has been completed, making it hard for the user to fix.

for example:

import autofig

autofig.plot([1], [2], linestyle='notvalid')
print(autofig.gcf().calls)
# show 0 entries
print(autofig.gcf().axes[0].calls
# shows 1 entry
autofig.draw()
# fails

The error message needs to be clearer, stating whether the call has been added or not and how to fix.