fsmonitor: normalize Watchman paths to bytes

Otherwise it will be a str on Python 3 and operations below
which operate in the bytes domain will fail.

Differential Revision: https://phab.mercurial-scm.org/D7211

hgext/fsmonitor/__init__.py

@@ -407,8 +407,15 b' def overridewalk(orig, self, match, subr'
     # for name case changes.
     for entry in result[b'files']:
         fname = entry[b'name']
+
+        # Watchman always give us a str. Normalize to bytes on Python 3
+        # using Watchman's encoding, if needed.
+        if not isinstance(fname, bytes):
+            fname = fname.encode(_watchmanencoding)
+
         if _fixencoding:
             fname = _watchmantofsencoding(fname)
+
         if switch_slashes:
             fname = fname.replace(b'\\', b'/')
         if normalize: