nemo-odf-to-txt: fix IndexError in handle_data on leading text:s tag

[leigh123linux]

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2520985

leigh@mpd-pc:~/Desktop/nemo/search-helpers (fix-odf-helper)$ python3 /usr/bin/nemo-odf-to-txt repro.odg
Traceback (most recent call last):
  File "/usr/bin/nemo-odf-to-txt", line 41, in <module>
    parser.feed(contents)
    ~~~~~~~~~~~^^^^^^^^^^
  File "/usr/lib64/python3.14/html/parser.py", line 187, in feed
    self.goahead(0)
    ~~~~~~~~~~~~^^^
  File "/usr/lib64/python3.14/html/parser.py", line 271, in goahead
    self.handle_data(unescape(rawdata[i:j]))
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/bin/nemo-odf-to-txt", line 26, in handle_data
    self.parsed[-1] += " " + data
    ~~~~~~~~~~~^^^^
IndexError: list index out of range
leigh@mpd-pc:~/Desktop/nemo/search-helpers (fix-odf-helper)$ python3 nemo-odf-to-txt repro.odg
content: hello world

leigh@mpd-pc:~/Desktop/nemo/search-helpers (fix-odf-helper)$ 

test file to reproduce crash

repro.odg