smtp: fix file_data inspection

Continue tracking data if API is used with detect. Detection engine
then manages the tracking.

Bug #2395.

src/util-file.c

@@ -609,7 +609,8 @@ static int FileAppendDataDo(File *ff, const uint8_t *data, uint32_t data_len)
         SCReturnInt(-1);
     }
 
-    if (FileStoreNoStoreCheck(ff) == 1) {
+    if ((ff->flags & FILE_USE_DETECT) == 0 &&
+            FileStoreNoStoreCheck(ff) == 1) {
 #ifdef HAVE_NSS
         int hash_done = 0;
         /* no storage but forced hashing */