mesa/st: Avoid spurious transfers when creating fbo textures without image data.
mesa/st: Avoid spurious transfers when creating fbo textures without image data.

We could actually try to do an early return both for gallium textures and
malloc memory textures, but I'm not sure exactly which situations
stImage->pt is NULL, and whether texImage->Data == NULL would be acceptible
or not.

Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>

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