server/mjpeg_encoder: realloc encoder->row, when a wider frame is given
server/mjpeg_encoder: realloc encoder->row, when a wider frame is given

Fix crashes when there are sized wider frames in the stream, and we are
linked with libjpeg.

Related : rhbz#813826
Resolves: rhbz#820669

dezelin/spice,ya-mouse/spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,dezelin/spice,Fantu/spice,SPICE/spice,SPICE/spice,fgouget/spice,Fantu/spice,fgouget/spice,alon/spice-server,alon/spice-server,fgouget/spice,elmarco/spice,Fantu/spice,mathslinux/spice,mathslinux/spice,mathslinux/spice,mathslinux/spice,elmarco/spice,alon/spice-server,alon/spice-server,SPICE/spice,dezelin/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,dezelin/spice,dezelin/spice,elmarco/spice,mathslinux/spice,fgouget/spice,ya-mouse/spice,alon/spice-server,elmarco/spice