indeo5: Fix null pointer dereference.

Bug found by: Oana Stratulat
Signed-off-by: Janne Grunau <janne-libav@jannau.net>

libavcodec/ivi_common.c

@@ -611,6 +611,9 @@ void ff_ivi_output_plane(IVIPlaneDesc *plane, uint8_t *dst, int dst_pitch)
     const int16_t   *src  = plane->bands[0].buf;
     uint32_t        pitch = plane->bands[0].pitch;
 
+    if (!src)
+        return;
+
     for (y = 0; y < plane->height; y++) {
         for (x = 0; x < plane->width; x++)
             dst[x] = av_clip_uint8(src[x] + 128);