[SVG] Set marker's fill attribute to black if it's none

Bug: https://bugs.documentfoundation.org/show_bug.cgi?id=47446

Commits:

1. https://cgit.freedesktop.org/libreoffice/core/commit/?id=644ace4143fe2576bfd71c8ab3da9d666d6523bb
2. https://cgit.freedesktop.org/libreoffice/core/commit/?id=1868a62a32cff30e3ba214cbd03917d2c6518073
3. https://cgit.freedesktop.org/libreoffice/core/commit/?id=de32fe50299a8891102528379e291919d2b66f56
4. https://cgit.freedesktop.org/libreoffice/core/commit/?id=1250acb00fbafb1afaa2d49c627feb9f07f60c3c

Sample File: https://bugs.documentfoundation.org/attachment.cgi?id=122919

Results:

Libreoffice 5.1

Libreoffice 5.2