revlog: adapt the `reading` check for `unionrepo`
We cannot just rely on the length check for the `unionrepo` as the local revlog
might be empty while the other revlog contains data. In addition, we need to
also open the second revlog for reading when needed.
# mock out util.makedate() to supply testable values
import os
from mercurial import pycompat
from mercurial.utils import dateutil
def mockmakedate():
filename = os.path.join(os.environ['TESTTMP'], 'testtime')
try:
with open(filename, 'rb') as timef:
time = float(timef.read()) + 1
except IOError:
time = 0.0
with open(filename, 'wb') as timef:
timef.write(pycompat.bytestr(time))
return (time, 0)
dateutil.makedate = mockmakedate