Recover from situations where the maximum canvas size is exceeded

On HiDPI devices or displays with very high resolutions, it can happen that zooming or rotating the map exceeds the maximum possible canvas size. In such cases (at least on iPads), the map completely disappears and cannot be brought back. Until we have a better fix (e.g. canvas tiles or stripes instead of a single canvas), at least after zooming or resetting the rotation, the map should be visible again.

See https://groups.google.com/d/msg/ol3-dev/ydA_0uW7F7Q/pA4JAwCXB28J for more details on this problem.