Fixed can't concat str to byte inside move

`os.path.basename` returns the same type that was used.

So, I have no guarantee that I needed here: `b'.''` or `'.'`.

Let use something universal ;)

Closes beetbox#4168

beets/util/__init__.py

@@ -495,9 +495,9 @@ def move(path, dest, replace=False):
     try:
         os.replace(path, dest)
     except OSError:
-        tmp = tempfile.mktemp(suffix='.beets',
-                              prefix=py3_path(b'.' + os.path.basename(dest)),
-                              dir=py3_path(os.path.dirname(dest)))
+        tmp = tempfile.mktemp(suffix=py3_path('.beets'),
+                              prefix=py3_path('.') + os.path.basename(py3_path(dest)),
+                              dir=os.path.dirname(py3_path(dest)))
         tmp = syspath(tmp)
         try:
             shutil.copyfile(path, tmp)