de95bf52cb Use checked_sub (Tobin C. Harding)
Pull request description:
Recently we "if" guarded subtraction manually using `> 0`, we can better convey the meaning by using `checked_sub` and pattern match on the option.
Refactor only, no logic changes.
ACKs for top commit:
RCasatta:
utACK de95bf52cb
apoelstra:
ACK de95bf52cb
Tree-SHA512: 2514cc2d8af89158e5e5e5a866f3fadb4927ba07dfb4e077fd16a98acf638588bee5ce03e2dc73fbda0b5064c30d8773d3be583c03c2a5336b8738c212a9776f