Minor MPL drawing sizing fix

[albi3ro]

In PR #4957 , I added extra space to the matplotlib figure and axes so they could accommodate classical wires without looking odd.

But the extra space was always there, whether or not we actually had any classical wires. This cropped up when comparing figure outputs from the qml demos.

This just makes the extra space conditional on the existence of classical wires, so that previous images will continue looking the same.

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (v0.34.0-rc0@147d565). Click here to learn what that means.

Additional details and impacted files

@@              Coverage Diff               @@
##             v0.34.0-rc0    #4987   +/-   ##
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  Coverage               ?   99.67%           
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  Files                  ?      392           
  Lines                  ?    35289           
  Branches               ?        0           
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  Hits                   ?    35174           
  Misses                 ?      115           
  Partials               ?        0           

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[timmysilv]

awesome, ty!