context: small refactoring of `isintroducedafter`

This make the next change clearer.

mercurial/context.py

@@ -763,8 +763,10 b' class basefilectx(object):'
     def isintroducedafter(self, changelogrev):
         """True if a filectx has been introduced after a given floor revision
         """
-        return (self.linkrev() >= changelogrev
-                or self._introrev() >= changelogrev)
+        if self.linkrev() >= changelogrev:
+            return True
+        introrev = self._introrev()
+        return introrev >= changelogrev
 
     def introrev(self):
         """return the rev of the changeset which introduced this file revision