rsvg-load.c: Accumulate to a GByteArray, not a GMemoryInputStream
rsvg-load.c: Accumulate to a GByteArray, not a GMemoryInputStream

The latter has O(n^2) behavior when appending lots of small buffers;
it's simply a GSList of GBytes (!).

So, now we use a GByteArray as a buffer, which we pass on in one chunk
at the end to the stream reader.

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg