ftp: point truncated lines at the unconsumed remainder

When a line exceeds the configured maximum length and contains no LF,
FTPGetLineForDirection emitted a window starting at the beginning of the
stream slice rather than at the unconsumed remainder. If a complete
command had already been taken from the same slice, that window was
shifted left by the consumed count: it began inside the previous command
and stopped short of the end of the long one.

The command MPM match, the per-transaction request copy and the port_line
capture all ran over those stale bytes, so a long command hidden behind a
short one in the same segment was classified and logged as the previous
command. The response direction had the same problem.

The LF-found branch already derives the line from input->buf + o_consumed;
do the same here, and advance consumed so the cursor still describes the
slice it was handed.

Issue: 8859

src/app-layer-ftp.c

@@ -290,9 +290,12 @@ static AppLayerResult FTPGetLineForDirection(
     if (lf_idx == NULL) {
         if (!(*current_line_truncated) && (uint32_t)input->len >= ftp_max_line_len) {
             *current_line_truncated = true;
-            line->buf = input->buf;
+            line->buf = input->buf + input->consumed;
             line->len = ftp_max_line_len;
             line->delim_len = 0;
+            /* No caller reads consumed after this; advance it so the cursor
+             * still describes the slice it was handed. */
+            input->consumed += input->len;
             input->len = 0;
             SCReturnStruct(APP_LAYER_OK);
         }