Window/canvas dimensions set to 0,0 due to floating point precision issue.

[kindjie]

In some instances, it seems the check for whether there's CSS sizing the canvas can fail in Emscripten_CreateWindow(). This makes it seem like the canvas disappears when a window is created.

The cause is that the retrieved values for css_w and css_h can be just under 1.0. The following floor() then returns 0.0 instead of 1.0, which sets external_size to true. The 0,0 dimensions is then carried through the creation of the window.

A work around is to set the canvas size in CSS, but to fix it a more robust check should be made in Emscripten_CreateWindow().