Fix memory leak when load_from_binary raises

ibf_load_code will leak memory allocated for the code if an exception is
raised. The following script reproduces the leak:

    bin = RubyVM::InstructionSequence.of(1.method(:abs)).to_binary

    10.times do
      100_000.times do
        RubyVM::InstructionSequence.load_from_binary(bin)
      rescue ArgumentError
      end
      puts `ps -o rss= -p #{$$}`
    end

Before:

    18004
    23380
    28756
    34260
    39892
    45396
    50772
    55892
    61012
    66132

After:

    12536
    12920
    13304
    13688
    14072
    14456
    14840
    15352
    15608
    15864

0 files changed, 0 insertions, 0 deletions