UnaryOp doesn't work on ARM devices

[arnaudbrejeon]

I found that my networks were failing on ARM devices and traced it to UnaryOp.
In function UnaryOp_arm::forward_inplace, I have opt.use_packing_layout is false and elempack is 1. The function will then just return 0.

I think its final return should be:
return UnaryOp::forward_inplace(bottom_top_blob, opt);

[nihui]

thanks for your report
the 20190906 release will be replaced by 20190908 soon