libopenjpegdec.c: Correctly scale gray16 output if precision < 16

Fixes ticket #2943.
Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>

libavcodec/libopenjpegdec.c

@@ -207,12 +207,16 @@ static inline void libopenjpeg_copyto16(AVFrame *picture, opj_image_t *image) {
     int *comp_data;
     uint16_t *img_ptr;
     int index, x, y;
+    int adjust[4];
+    for (x = 0; x < image->numcomps; x++)
+        adjust[x] = FFMAX(FFMIN(16 - image->comps[x].prec, 8), 0);
+
     for (index = 0; index < image->numcomps; index++) {
         comp_data = image->comps[index].data;
         for (y = 0; y < image->comps[index].h; y++) {
             img_ptr = (uint16_t*) (picture->data[index] + y * picture->linesize[index]);
             for (x = 0; x < image->comps[index].w; x++) {
-                *img_ptr = *comp_data;
+                *img_ptr = *comp_data << adjust[index];
                 img_ptr++;
                 comp_data++;
             }