Suricata smtp/mime: heap out-of-bounds read quoted-printable decoder

Suricata is a network Intrusion Detection System, Intrusion Prevention System and Network Security Monitoring engine. From 7.0.13 until 7.0.17, the SMTP MIME quoted-printable decoder in src/util-decode-mime.c can read one byte past a heap buffer when a quoted-printable escape sequence is split across traffic chunks and the following chunk contains exactly one byte. Crafted SMTP traffic can trigger the out-of-bounds read and crash Suricata when decode-quoted-printable MIME decoding is enabled. This issue is fixed in version 7.0.17.