Don't fail on empty LocalStatus cache files

As reported in https://github.com/spaetz/offlineimap/pull/2, we would
fail when files are empty because file.read() would throw attribute
errors.

Fix this by removing the superfluous read() check and additionally log
some warning message.

Reported-by: Ralf Schmitt
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/folder/LocalStatus.py

@@ -65,9 +65,11 @@ class LocalStatusFolder(BaseFolder):
         file = open(self.filename, "rt")
         self.messagelist = {}
         line = file.readline().strip()
-        if not line and not line.read():
+        if not line:
             # The status file is empty - should not have happened,
             # but somehow did.
+            errstr = "Cache file '%s' is empty. Closing..." % self.filename
+            self.ui.warn(errstr)
             file.close()
             return
         assert(line == magicline)