Empty tags about ofxparse HOT 6 OPEN

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.7/bin/hledger-autosync", line 11, in <module>
    sys.exit(run())
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/ledgerautosync/cli.py", line 311, in run
    import_ofx(ledger, args)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/ledgerautosync/cli.py", line 114, in import_ofx
    ofx = OfxSynchronizer.parse_file(args.PATH)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/ledgerautosync/sync.py", line 41, in parse_file
    return OfxParser.parse(open(path))
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/ofxparse/ofxparse.py", line 432, in parse
    ofx_obj.accounts += cls.parseStmtrs(stmtrs_ofx, AccountType.Bank)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/ofxparse/ofxparse.py", line 818, in parseStmtrs
    account.curdef = act_curdef.contents[0].strip()
IndexError: list index out of range

 <TRNTYPE>Credit</TRNTYPE>
 <DTPOSTED>20180801</DTPOSTED>
 <TRNAMT>0.0</TRNAMT>
 <FITID></FITID>
 <VALUEDATE>20180801</VALUEDATE>
 <NAME></NAME>
 <TRANSACTIONSPLIT>No</TRANSACTIONSPLIT>
 <CATEGORY>Uncategorised</CATEGORY>
 <ACCTBAL>-400.52</ACCTBAL>
 <CHECKNUM></CHECKNUM>
 <REFNUM></REFNUM>
 <MEMO>NEW INTEREST RATE  3.870%</MEMO>
 <CURRENCY>
  <CURRATE>1.0000</CURRATE>
  <CURSYM>AUD</CURSYM>
 </CURRENCY>
</STMTTRN>```

and

```<STMTTRN>
<TRNTYPE>DEBIT
<DTPOSTED>20180801
<DTUSER>20180801
<TRNAMT>-10.00
<FITID>
<MEMO>Account Fee
</STMTTRN>```

Both have empty FITID fields. One has empty NAME field. Either empty or missing CHECKNUM and REFNUM fields.

Since transactions can be parsed by ofxparse if CHECKNUM, REFNAME, NAME and FITID are missing, empty fields should be handled in the same way.

Will try and put together a PR for these in the next few days.