Suricata

In SMTPProcessCommandDATA() (src/app-layer-smtp.c), the return value of
FileAppendData() is ignored in the raw_extraction branch. When FileAppendData
fails (e.g. due to memory allocation failure in the streaming buffer), the
file silently transitions to FILE_STATE_ERROR without any diagnostic log
message. This leads to incomplete file inspection and potential missed
detections.

In 6 out of 7 other call sites in the codebase, the return value of
FileAppendData is checked. Neighbouring file operations in the same file
(FileOpenFileWithId, FileCloseFile) also explicitly handle errors.

Fix: store the return value and log a debug message on failure.

Flagged by Svace static analyzer (UNCHECKED_FUNC_RES.STAT).

PR: https://github.com/OISF/suricata/pull/15721