truemotion1: make sure index does not go out of bounds

Fixes invalid reads.
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org

libavcodec/truemotion1.c

@@ -515,6 +515,15 @@ hres,vres,i,i%vres (0 < i < 4)
     index = s->index_stream[index_stream_index++] * 4; \
 }
 
+#define INC_INDEX                                                   \
+do {                                                                \
+    if (index >= 1023) {                                            \
+        av_log(s->avctx, AV_LOG_ERROR, "Invalid index value.\n");   \
+        return;                                                     \
+    }                                                               \
+    index++;                                                        \
+} while (0)
+
 #define APPLY_C_PREDICTOR() \
     predictor_pair = s->c_predictor_table[index]; \
     horiz_pred += (predictor_pair >> 1); \
@@ -527,10 +536,10 @@ hres,vres,i,i%vres (0 < i < 4)
             if (predictor_pair & 1) \
                 GET_NEXT_INDEX() \
             else \
-                index++; \
+                INC_INDEX; \
         } \
     } else \
-        index++;
+        INC_INDEX;
 
 #define APPLY_C_PREDICTOR_24() \
     predictor_pair = s->c_predictor_table[index]; \
@@ -544,10 +553,10 @@ hres,vres,i,i%vres (0 < i < 4)
             if (predictor_pair & 1) \
                 GET_NEXT_INDEX() \
             else \
-                index++; \
+                INC_INDEX; \
         } \
     } else \
-        index++;
+        INC_INDEX;
 
 
 #define APPLY_Y_PREDICTOR() \
@@ -562,10 +571,10 @@ hres,vres,i,i%vres (0 < i < 4)
             if (predictor_pair & 1) \
                 GET_NEXT_INDEX() \
             else \
-                index++; \
+                INC_INDEX; \
         } \
     } else \
-        index++;
+        INC_INDEX;
 
 #define APPLY_Y_PREDICTOR_24() \
     predictor_pair = s->y_predictor_table[index]; \
@@ -579,10 +588,10 @@ hres,vres,i,i%vres (0 < i < 4)
             if (predictor_pair & 1) \
                 GET_NEXT_INDEX() \
             else \
-                index++; \
+                INC_INDEX; \
         } \
     } else \
-        index++;
+        INC_INDEX;
 
 #define OUTPUT_PIXEL_PAIR() \
     *current_pixel_pair = *vert_pred + horiz_pred; \