remove trailing decimal point in format_satoshis

[myxmaster]

If "Zeros after decimal point" in Preferences is set to 0 and the amount is an integer (e.g. 1), it is currently displayed as 1. which looks weird. This pull request removes the trailing decimal point in this case.

I noticed the help dialog for "Zeros after decimal point" says explicitly "1." too, so not sure if this was on purpose? I'd strongly suggest to drop the . in this case...