dma: use canonical getline() loop

[emaste]

Summary

getline() returns -1 on erorr or EOF, so just use that condition instead of feof().

[emaste]

add errno check

[emaste]

related upstream discussion in https://github.com/corecode/dma/issues/18

[emaste]

Missing {

[bapt]

I don't know why I went the complicated way in the first place ;)

[emaste]

explicitly set errno = 0 before loop; getline() leaves it unchanged upon EOF

[emaste]

use ferror rather than futzing with errno