The sps_t structure contains an array of 64 short_term_ref_pic_sets_t
elements. Therefore at most 63 may be added to the base pointer
short_term_ref_pic_sets for accessing one of those elements.
Fixes the following test cases of #1780:
explorer🆔000494,sig:11,src:001249,op:flip1,pos:63
explorer🆔000496,sig:06,src:001249,op:flip1,pos:92
explorer🆔000502,sig:06,src:001249,op:int8,pos:100,val:+32
explorer🆔000605,sig:11,src:001741,op:int32,pos:29,val:+0
explorer🆔000676,sig:06,src:002253,op:ext_AO,pos:101
explorer🆔000784,sig:11,src:002818,op:ext_AO,pos:103
explorer🆔000830,sig:11,src:003020,op:flip1,pos:103
explorer🆔000831,sig:11,src:003020,op:flip1,pos:104
explorer🆔000834,sig:11,src:003020,op:havoc,rep:2
explorer🆔000882,sig:11,src:003246,op:flip1,pos:123
explorer🆔000884,sig:11,src:003246,op:int8,pos:121,val:-128
explorer🆔000886,sig:06,src:003248,op:flip1,pos:106
explorer🆔000935,sig:11,src:003528,op:flip4,pos:130
explorer🆔000936,sig:11,src:003528,op:flip32,pos:127
explorer🆔000937,sig:11,src:003528,op:arith8,pos:130,val:+5
explorer🆔000938,sig:11,src:003528,op:int32,pos:127,val:+100
explorer🆔000939,sig:11,src:003528,op:int32,pos:128,val:+1
explorer🆔000974,sig:11,src:003742,op:flip1,pos:123
explorer🆔000975,sig:11,src:003746,op:flip1,pos:130
explorer🆔000976,sig:11,src:003746,op:flip1,pos:130
explorer🆔000977,sig:11,src:003746,op:flip1,pos:133
explorer🆔000978,sig:11,src:003746,op:flip1,pos:133
explorer🆔000979,sig:11,src:003746,op:flip2,pos:134
explorer🆔000980,sig:11,src:003746,op:arith8,pos:133,val:-3
explorer🆔001003,sig:11,src:003976,op:flip1,pos:127
explorer🆔001019,sig:11,src:004180,op:flip1,pos:9
explorer🆔001020,sig:11,src:004180,op:int32,pos:143,val:be:+1
explorer🆔001021,sig:11,src:004180,op:havoc,rep:2
