[cogl-texture] Set GL_PACK_ROW_LENGTH when downloading texture data
[cogl-texture] Set GL_PACK_ROW_LENGTH when downloading texture data

Otherwise the rowstride passed in from an application is not used
correctly so you can not download to an area with a much larger
rowstride.

gcampax/cogl,spatulasnout/cogl,gcampax/cogl,gcampax/cogl,Distrotech/cogl,djdeath/cogl,Distrotech/cogl,Distrotech/cogl,djdeath/cogl,Distrotech/cogl,collects/cogl,spatulasnout/cogl,djdeath/cogl-android,djdeath/cogl-android,collects/cogl,djdeath/cogl,gcampax/cogl,djdeath/cogl-android