PIR version of Buf concatenation segfault

buf.pir

.sub bb
    $P0 = new 'ByteBuffer'
    $P0 = 100
    $I0 = 0
  loop:
    $I1 = $I0 + 1
    $P0[$I0] = $I1
    inc $I0
    unless $I0 == 100 goto loop
    .return ($P0)
.end

.sub main :main
    $P0 = new 'ByteBuffer'
    $P0 = 1
    $P0[0] = 1
    $I0 = 0
loop:
    $P1 = 'bb'()
    $S0 = $P0.'get_string'('binary')
    $S1 = $P1.'get_string'('binary')
    $S0 = concat $S0, $S1
    $P0 = new 'ByteBuffer'
    $P0 = $S0
    inc $I0
    unless $I0 == 1000 goto loop
.end

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