Guard out of boundary write in rate allocation

This fixes an encoder crash issue due to out-of-boundary write
in GOP construction. This happens when a large chunk of frames
are static and the encoder decides to use maximum GOP length.

BUG=b/182490901

STATS_CHANGED

Change-Id: I8a7925af244f066b48ff5dd9256bf9891a807a70
(cherry picked from commit 169849bea5c983abce9f998547c93d94063240a8)

av1/encoder/pass2_strategy.c

diff --git a/av1/encoder/pass2_strategy.c b/av1/encoder/pass2_strategy.c
index b1c52bd..482e260 100644
--- a/av1/encoder/pass2_strategy.c
+++ b/av1/encoder/pass2_strategy.c
@@ -943,7 +943,8 @@
   // in the next GOP. For GF group, next GOP will overwrite the rate allocation.
   // Setting this frame to use 0 bit (of out the current GOP budget) will
   // simplify logics in reference frame management.
-  gf_group->bit_allocation[gf_group_size] = 0;
+  if (gf_group_size < MAX_STATIC_GF_GROUP_LENGTH)
+    gf_group->bit_allocation[gf_group_size] = 0;
 }
 
 // Returns true if KF group and GF group both are almost completely static.