Crash when loading FastConv HRTF file

When using the -hrtf option at the decoder with a binary file that contains only FastConv ROM data, the decoder crashes trying to copy BRIR data to a null pointer.

Example to reproduce:

./IVAS_cod -sba 3 512000 48 scripts/testv/stv3OA48c.wav bit
./IVAS_dec -hrtf scripts/binauralRenderer_interface/binaural_renderers_hrtf_data/fastconv_HRIR_128_Meth5_IRC_53_Q10_symL_Itrp1_48000_IIS_BRIR_officialMPEG_Combined.bin BINAURAL 48 bit /dev/null

fastconv_HRIR_128_Meth5_IRC_53_Q10_symL_Itrp1_48000_IIS_BRIR_officialMPEG_Combined.bin