remove a source of confusion

make sure raw texts never include empty strings

make sure batch size is set correctly, if only inpainting images are …

…passed in, for unconditional image synthesis. also allow for forcing unconditional image synthesis on network trained conditionally, although not recommended

add an extra assert to make sure researcher / user cannot sample with…

…out text on a network with cross attention blocks

fix ddp and self conditioning in elucidated ddpm

make sure self conditining works in distributed training, cleanup lat…

…er, bump

fix a bug with inpainting for non-elucidated ddpm

allow for one to pass in a tuple to use_linear_attn kwargs in unet, t…

…o finely specify which layers get sparse linear attention, and to turn off attention altogether