3961: Fix double comma when merge imports on second line r=edwin0cheng a=IceSentry
This fixes the bug when merging imports from the second line when it already has a comma it would previously insert a comma.
There's probably a better way to check for a COMMA.
This also ends up with a weird indentation, but rust-fmt can easily deal with it so I'm not sure how to resolve that.
Closes#3832
Co-authored-by: IceSentry <c.giguere42@gmail.com>