MAINT: Only calc inverse ratio if it applies.
MAINT: Only calc inverse ratio if it applies.

Avoid unneeded work by only calcultaing the inverse ratio when it
applies to the current range.

humdings/zipline,quantopian/zipline,alphaBenj/zipline,magne-max/zipline-ja,Scapogo/zipline,alphaBenj/zipline,florentchandelier/zipline,bartosh/zipline,bartosh/zipline,enigmampc/catalyst,humdings/zipline,enigmampc/catalyst,magne-max/zipline-ja,quantopian/zipline,florentchandelier/zipline,Scapogo/zipline