Init folder list early enough

We need the list of folders and the folder delimiter, but it was not
always retrieved early enough. E.g. when doing IMAP<->IMAP sync and the
local IMAP being readonly, we would bunk out with a mysterious error
message become repository.getsel() would still return None.

This commit fixes this error.

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

Changelog.draft.rst

@@ -31,3 +31,8 @@ Changes
 
 Bug Fixes
 ---------
+
+* IMAP<->IMAP sync with a readonly local IMAP repository failed with a
+  rather mysterious "TypeError: expected a character buffer object"
+  error. Fix this my retrieving the list of folders early enough even
+  for readonly repositories.

offlineimap/accounts.py

@@ -274,6 +274,13 @@ class SyncableAccount(Account):
             remoterepos = self.remoterepos
             localrepos = self.localrepos
             statusrepos = self.statusrepos
+
+            # init repos with list of folders, so we have them (and the
+            # folder delimiter etc)
+            remoterepos.getfolders()
+            localrepos.getfolders()
+            statusrepos.getfolders()
+
             # replicate the folderstructure between REMOTE to LOCAL
             if not localrepos.getconfboolean('readonly', False):
                 self.ui.syncfolders(remoterepos, localrepos)