Fix #1616: NNPFC SEI nnpfc_chroma_sample_loc_type_frame value is checked even when not signalled

When nnpfc_chroma_loc_info_present_flag is zero, nnpfc_chroma_sample_loc_type_frame is not present in the NNPFC SEI. Regardless of this, the value of nnpfc_chroma_sample_loc_type_frame is checked at the decoder. The check should be done at encoder and decoder, but only if the syntax element is present in the NNPFC SEI.