Created attachment 214560 [details] [review]
Patch for convert_to_double() segmentation fault

When building babl 0.1.10 on NetBSD/sparc64, the generation of
BablFishPath.html in the docs directory fails, because
babl_fish_path_dhtml receives a segmentation fault.

The problem occurs in babl/babl-fish-reference.c:convert_to_double()
because of the call to babl_process() when dst_img->data[0] might be
null.  This happens part way through processing the html, when no
match is found for source_fmt->component[i] when i = 0 (the match
occurs when i = 1 and j = 0).  This causes the call to babl_process()
without first assigning dst_img->data[0] .

The attached patch seems to fix the problem, but I don't know if it's
correct (i.e. is the case where no match is found when i = 0 valid?).