copies: avoid calling matcher if matcher.always() When storing copy information in the changesets (experimental.copies.read-from=changeset-only), this patch speeds up hg debugpathcopies FENNEC_58_0_2_BUILD1 FIREFOX_59_0b8_BUILD2 from 5.9s to 4.7s. At the start of this series (b162229e), that command took 18min. Differential Revision: https://phab.mercurial-scm.org/D6422