Fix autocompletion endless loop for last line in file

[abobov]

Error can be reproduced on this file:

2019/07/01 Transaction
    Assets                                 $100.00
    Income

2019-07-02 T<C-x><C-o>

Line 2019-07-02 T should be last line in a file (no blank line after it) and then you try to compete transaction name it's would run endless loop.

[alerque]

Thank you for fixing this! I had actually run into this and failed to trace it in any meaningful way. I wasn't even sure it was this plugin or something else I had going on.