Revert "Prevent access of array using -1 index"

This reverts commit 38cdce8eb9896b01b4c0b635aea03548520ddd8f.

Reason for revert: <INSERT REASONING HERE>

It is reported that this introduced a segment fault, revert now to investigate. 

Change-Id: I229dcdc09462ae4eb9cf2a3da4ce59aa9eafe65e

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index ef2bdb2..5950f19 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -2135,7 +2135,7 @@
       partition_plane_context(xd, mi_row, mi_col, has_rows, has_cols, bsize);
   const aom_prob *const probs =
       ctx < PARTITION_CONTEXTS ? cm->fc->partition_prob[ctx] : NULL;
-  FRAME_COUNTS *const counts = ctx >= 0 ? xd->counts : NULL;
+  FRAME_COUNTS *const counts = ctx < PARTITION_CONTEXTS ? xd->counts : NULL;
 #else
   const int ctx = partition_plane_context(xd, mi_row, mi_col, bsize);
   const aom_prob *const probs = cm->fc->partition_prob[ctx];

av1/encoder/encodeframe.c

diff --git a/av1/encoder/encodeframe.c b/av1/encoder/encodeframe.c
index 04265fd..a84322a 100644
--- a/av1/encoder/encodeframe.c
+++ b/av1/encoder/encodeframe.c
@@ -3304,7 +3304,7 @@
 #endif
                                          bsize);
 #endif  // CONFIG_CB4X4
-  const int *partition_cost = pl >= 0 ? x->partition_cost[pl] : NULL;
+  const int *partition_cost = x->partition_cost[pl];
 #if CONFIG_SUPERTX
   int this_rate_nocoef, sum_rate_nocoef = 0, best_rate_nocoef = INT_MAX;
   int abort_flag;