Bug#627482: Same function, slightly different crash

[Noel Duffy]

This crash happened at the end of level 12, just when the second guardian
was defeated. The crash happened on line 1090 compared with 1081 the last
time. This time it's the screen8 pointer which has gone out of bounds.

-- begin gdb output

Program received signal SIGSEGV, Segmentation fault.
0x00000000004462b5 in sprite_object::draw_with_tables (this=0x2bdb540)
    at sprite_object.cc:1090
1090              *(screen8++) = p;
(gdb) bt
#0  0x00000000004462b5 in sprite_object::draw_with_tables (this=0x2bdb540)
    at sprite_object.cc:1090
#1  0x00000000004460ed in sprite_object::draw (this=0x2bdb540)
    at sprite_object.cc:1034
#2  0x00000000004372e6 in list_sprites::draw (this=0x2840040)
    at list_sprites.cc:158
#3  0x0000000000453625 in supervisor_guards_level::main_loop (this=0x2a0b940)
    at supervisor_guards_level.cc:302
#4  0x0000000000458724 in tecnoballz::game_begin () at tecnoballz.cc:141
#5  0x00000000004374a3 in main (arg_count=1, arg_values=0x7ffffa9b3f48)
    at main.cc:86
(gdb) info locals
p = -103 '\231'
j = 0
k = 1
pixels8 = 0x2a29971 
"!\252\235`\221\221\275\221\231\221\221\221`\221\331`\221\252A\221\221\235`\221\221\221\221!!\221"

screen8 = 0x10289a7d7 <Address 0x10289a7d7 out of bounds>
i = 0
screen32 = 0x10289a7d7
pixels32 = 0x2a29970
counters = 0x2bd9218
h = 12