Previously, debug info would refer to the first file seen, even
when it did not actually generate line numbers (e.g. segto=-1).
Fix it so we only lock in the file name the first time we actually
produce a line number record. Not as good as proper support for
debug info referencing multiple source files but much more useful
than the current behavior.
Signed-off-by: Fabian Giesen <fabiang@radgametools.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>