Allow larger precision any time UTC jds are near zero.
Allow larger precision any time UTC jds are near zero.

And add a bit more clarification for the two places where this
can happen.

pllim/astropy,saimn/astropy,aleksandr-bakanov/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,astropy/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,astropy/astropy,pllim/astropy,mhvk/astropy,saimn/astropy,lpsinger/astropy,StuartLittlefair/astropy,larrybradley/astropy,mhvk/astropy,pllim/astropy,larrybradley/astropy,StuartLittlefair/astropy,lpsinger/astropy,dhomeier/astropy,pllim/astropy,lpsinger/astropy,saimn/astropy,StuartLittlefair/astropy,larrybradley/astropy,dhomeier/astropy,lpsinger/astropy,astropy/astropy,astropy/astropy,aleksandr-bakanov/astropy,mhvk/astropy,lpsinger/astropy,dhomeier/astropy,astropy/astropy,larrybradley/astropy,saimn/astropy,pllim/astropy,StuartLittlefair/astropy,saimn/astropy,mhvk/astropy,dhomeier/astropy,StuartLittlefair/astropy,mhvk/astropy