In Safari, bitmaps enlarged inside the editor AND in code still look blurry

[benjiwheeler]

The fixes to scaled bitmap blurriness in #385 worked great! But there's one case I found, on Mac Safari, where it doesn't seem to work.

Expected

1. edit a bitmap
2. enlarge it in the bitmap editor using handles
3. enlarge the sprite in the stage using the set size block or the size input
4. the bitmap should look crisp and not blurry.

Actual result:

Mac Mojave 10.14.2, Chrome Version 71.0.3578.98 looks great:

Mac Mojave 10.14.2, Firefox 64.0 looks great:

Mac Mojave 10.14.2, Safari 12.0.2 (14606.3.4) still looks blurry:

/cc @fsih, @cwillisf, @paulkaplan