#13 Fix scaling threading issue in AdvancedViewer

[Luke Wylie]

The rendered image from the JAI scaled op does not render before the image is set to the display.

[Dejan Vucinic]

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Don't know if this is the same issue, but images larger than 1000x1000
pixels display the first five-six times then disappear. Only the Bill
Gates fix works at that point to get the large images to display again.