Some video players can cope with that by displaying the line for some pre-defined amount of time, or until the next line begins. Kodi 16.1, on my HTPC, for one can't do that. So I wrote a Python script which takes subsequent line's start-frame, substracts 1 from it and replaces the missing end-frame with the result. For the last line in a file it just adds 99 frames to its start frame. This cuts it for me. You can get the code on my GitHub page. The command line help hopefully explains it all:
 
$ ./subs_add_stop_frame.py --help
usage: subs_add_stop_frame.py [--help] [--encoding STRING] --input PATH
                              --output PATH
Add missing MicroDVD subtitle line's stop-frames based on subsequent subtitle
line's start-frame.
Arguments:
  --help             Show this help message and exit.
  --encoding STRING  Input subtitles encoding - one of
                     https://docs.python.org/2/library/codecs.html#standard-
                     encodings. By default the script tries to auto-detect it
                     using `chardet' library, but you may choose to specify it
                     here in case the magic fails.
  --input PATH       Input subtitles file path.
  --output PATH      Output subtitles file path.

Now when you run the script on the few example input lines I gave above, they become:
 
{100}{224}Chwila.
{225}{274}Ładnie.
{275}{324}Przyniosłem ci coś.
<snip>
{32100}{32274}Dobrze.
{32275}{32549}/- Och, Jack!|/- Och, Judy!
{32550}{32649}Tłumaczenie: Cholek

If you find it useful - enjoy. In case of a bug or something please let me know. Always happy to receive feedback.