Fix #114 Invalid memory reference with Filter::ia64

[ChanTsune]

Hi @alexcrichton

I resolved segmentation fault reported in issue #114

As for adding -D HAVE_DECODER_IA64=1 -D HAVE_ENCODER_IA64=1 added to the issue, another problem remains, there is a lack of macros to declare the use of encoders corresponding to each Filter That's the reason.
Filters::arm requires -D HAVE_DECODER_ARM=1 -D HAVE_ENCODER_ARM=1 and Filters::arm_thumb requires -D HAVE_DECODER_ARMTHUMB=1 -D HAVE_ENCODER_ARMTHUMB=1

I think a separate PR is appropriate for this. Also HAVE_DECODER_ARMTHUMB and HAVE_ENCODER_ARMTHUMB macros are added in #116