fix the in-place modification in unet condition when using controlnet (#2586)
* fix the in-place modification in unet condition when using controlnet, which will cause backprop errors when training
* add clone to mid block
* fix-copies
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Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
Co-authored-by: William Berman <WLBberman@gmail.com>