Internet Explorer seems to flag images as loaded prematurely, which
can result in rendering bugs. We can detect this by looking at the
dimensions though.
Commit 6e7e6f9 stopped the function from running if width or height was
zero, this commit reverts that change. This commit also makes the
resulting canvas 0x0 if autoscale is called with zero. By adding this
special case we can avoid division by zero in the calculations.
