zodbcommit: Fix stdin reading on py3

Zodbcommit reads input in zodbdump format from stdin and then uses
zodbdump.DumpReader to parser that input. The parser works on binary
data.

However zodbcommit, was preparing that input data mixing bytes and
strings, which is failing on py3:

    (py3.venv) kirr@deca:~/src/wendelin/z/zodbtools$ zodb commit 1.fs 00
    Ignoring index for /home/kirr/src/wendelin/z/zodbtools/1.fs
    aaa
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/py3.venv/bin/zodb", line 33, in <module>
        sys.exit(load_entry_point('zodbtools', 'console_scripts', 'zodb')())
      File "/home/kirr/src/wendelin/z/zodbtools/zodbtools/zodb.py", line 129, in main
        return command_module.main(argv)
      File "/home/kirr/src/wendelin/venv/py3.venv/lib/python3.9/site-packages/decorator.py", line 232, in fun
        return caller(func, *(extras + args), **kw)
      File "/home/kirr/src/tools/go/pygolang/golang/__init__.py", line 103, in _
        return f(*argv, **kw)
      File "/home/kirr/src/wendelin/z/zodbtools/zodbtools/zodbcommit.py", line 222, in main
        zin += sys.stdin.read()
    TypeError: can't concat str to bytes

-> Fix it by reading stdin in binary mode.

No test currently as zodbcommit.main is not covered by tests (hopefully yet).

zodbtools/zodbcommit.py

-# Copyright (C) 2018-2021  Nexedi SA and Contributors.
+# Copyright (C) 2018-2022  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -40,7 +40,7 @@ can query current database head (last_tid) with `zodb info <stor> last_tid`.
 
 from __future__ import print_function
 from zodbtools import zodbdump
-from zodbtools.util import ashex, fromhex, storageFromURL
+from zodbtools.util import ashex, fromhex, storageFromURL, asbinstream
 from ZODB.interfaces import IStorageRestoreable
 from ZODB.utils import p64, u64, z64
 from ZODB.POSException import POSKeyError
@@ -219,7 +219,7 @@ def main(argv):
     # artificial transaction header with tid=0 to request regular commit
     zin = b'txn 0000000000000000 " "\n'
 
-    zin += sys.stdin.read()
+    zin += asbinstream(sys.stdin).read()
     zin = BytesIO(zin)
     zr = zodbdump.DumpReader(zin)
     zr.lineno -= 1                      # we prepended txn header