Only start padding with zeros at 10^n

[ginnyTheCat]

This makes sure 10 nodes still only have 1 digit as we are going from 0-9. The same applies to 100 or 1000 etc nodes ofc. Not a huge change, just a small polish.

Before:

After:

[joto]

Now the functionality is complex enough that it should go into its own function and get a unit test.

[joto]

And maybe we should just use snprintf to tell us how long the output will be? See second paragraph under Notes. Unless that's much more expensive than the log().

[joto]

I have fixed this in a242ddc with an extra function. Thanks @ginnyTheCat for reporting this and providing the fix.