`Image.Create()` does not zero allocated memory.

[p120ph37]

When Image.Create() is called, it may (if the existing buffer is not already large enough, or if no buffer yet exists) allocate a new buffer. It allocated the buffer without initializing it, so whatever data happens to be in memory already ends up in the image. This can lead at best to some weird images if the new memory happens to contain non-zero pre-existing data, and a security issue at worst if the image with uninitialized pixels is being output somewhere non-privileged. I'll file a PR to fix this.