In general, this issue results in incorrect intialisation of the editor's horizontal scrollbar (at least on my platform, see the Geany-INFO in OP)
Further debugging yields more pointers at the cause of this issue.
The warning seems to result from `Scintilla::ScintillaGTK::Resize()` call triggered by `sci_set_lines_wrapped()` during [`open_session_file()`](../geany/blob/402d277f80b508e89440fe3669ce3f2f45768cc7/src/keyfile.c#L1237) at start-up.
Precisely, the `editor_set_line_wrapping()` is what trips the warning:
https://github.com/geany/geany/blob/402d277f80b508e89440fe3669ce3f2f45768cc7...
From what I could understand, in this context the intent of this call is to properly configure the editor for each file re-loaded from the previous session. So the effect of this call should be setting of the `doc->editor->line_wrapping` from the previously saved state (from session file).
Indeed, amending this line into: ``` doc->editor->line_wrapping = line_wrapping ``` fixes the warning and corrects the initialisation of the scrollbar.
Looking closer at what this does, this change removes an extra Sci-call to `SSM(sci, SCI_SETWRAPMODE, SC_WRAP_WORD, 0)`, which requests a reset of the line-wrapping mode. In this context it appears to be unnecessary, as the correct line-wraping mode has been already set up during the creation of the document in `document_open_file_full()`, which subsequently calls `sci_set_lines_wrapped(sci, editor->line_wrapping)` from `create_new_sci()`:
https://github.com/geany/geany/blob/402d277f80b508e89440fe3669ce3f2f45768cc7...
Hope this is helpful. Perhaps, someone more familiar with this context could comment on the need for this seemingly redundant Sci-call. If this change indeed makes sense, I can produce a PR for it.