indeo: Reject impossible FRAMETYPE_NULL

A frame marked FRAMETYPE_NULL cannot be scalable and requires a
previous frame successfully decoded.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/ivi_common.c

@@ -958,6 +958,14 @@ int ff_ivi_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
                 }
             }
         }
+    } else {
+        if (ctx->is_scalable)
+            return AVERROR_INVALIDDATA;
+
+        for (p = 0; p < 3; p++) {
+            if (!ctx->planes[p].bands[0].buf)
+                return AVERROR_INVALIDDATA;
+        }
     }
 
     //STOP_TIMER("decode_planes"); }