rhg: small refactor: stop using a magical constant "+ 1"

Instead, directly do what the "+ 1" was supposed to achive:
call hash_encode.

rust/hg-core/src/revlog/path_encode.rs

@@ -600,7 +600,7 b' pub fn path_encode(path: &[u8]) -> Vec<u'
         basic_encode(&mut measure, path);
         measure.len
     } else {
-        MAXSTOREPATHLEN + 1
+        return hash_encode(path);
     };
     if newlen <= MAXSTOREPATHLEN {
         if newlen == path.len() {