detect: minor optimization for tx

do not bother to clean the buffers, if we did not run detection
for this transaction.

src/detect.c

@@ -1638,9 +1638,9 @@ static void DetectRunTx(ThreadVars *tv,
 
             StoreDetectFlags(&tx, flow_flags, ipproto, alproto, new_detect_flags);
         }
-next:
         InspectionBufferClean(det_ctx);
 
+    next:
         if (!ires.has_next)
             break;
     }