#2870 sdas uses the wrong file name for errors in some cases

[Alan Cox]

If you .include a file then instead of reporting the correct filename it reports the error with the right line number but as if it were in the .sym file of the original source or the original source name depending upon the options used

so sdasz80 a.asm reports an error in a.asm that is really in b.asm
sdasz80 -l a.asm reports it as in a.lst

(and so on - I suspect it's using the last generated name not the right one)