[#211] [Wires] Issues when using mediators (zoom, pan)

[karreiro]

See https://github.com/ahome-it/lienzo-core/issues/211

Incorporating the fix that was made here with @danielzhe's comment.

Could you please take a look @mdproctor?

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Part of an ensemble:

• https://github.com/ahome-it/lienzo-core/pull/218
• https://github.com/ahome-it/lienzo-tests/pull/22