Tested ok, except if the user enters 0 gets the warning: "(geany:6625): Geany-CRITICAL **: 10:51:24.814: editor_goto_line: assertion 'line_no >= 0' failed"
Scintilla docs for `gotoline` say numbered from 0 and thats the only place I can find that explicitly specifies it.
But the margins are numbered from 1 and entering a number goes to the start of the line with that margin number. Geany uses `getposfromline` and `gotopos` not `gotoline` so maybe that compensates in some way????? I'm confused.
Anyway maybe its better to only warn on < 0 and silently change 0 to 1 rather than give a warning for user input of 0.