multiline: ml: ensure context is registered for REGEX type

This fix ensures that when the buffer is
flushed, the record will have proper timestamp
and metadata instead of just the "log" field.

Signed-off-by: Mirko Lazarevic <[email protected]>

Author: mirko-lazarevic

src/multiline/flb_ml.c

@@ -268,6 +268,11 @@ static int package_content(struct flb_ml_stream *mst,
         if (ret == FLB_MULTILINE_TRUNCATED) {
             truncated = FLB_TRUE;
         }
+
+        if (stream_group->mp_sbuf.size == 0) {
+            flb_ml_register_context(stream_group, tm, full_map);
+        }
+
         processed = FLB_TRUE;
     }
     else if (type == FLB_ML_ENDSWITH) {