multi-exponentiation with single point is wrong about blst

[vmx]

I'm just forwarding bug reports ;) I agree though that it's meant for multiple things. Though it was still a bit unexpected to not getting an error, but really some unexpected result. Thanks for fixing!

[dot-asm]

Come on! It's in the name, multi, so 1 does not qualify-) But even on a serious note, formally speaking it shouldn't come as a surprise that a subroutine that expects multiple inputs doesn't handle one. But all right. I suppose if the library qsort works with a single input, then MSM could as well. Though the comparison is not really adequate. In the sense that if MSM did if (n ==1) return then you would complain, while qsort doing the same would qualify as doing-the-job. Sigh... Anyway, fixed.