htp: fix pointer check logic

Don't check pointer after it has already been used.

Coverity 1047545

src/app-layer-htp.c

@@ -1957,6 +1957,10 @@ void HTPFreeConfig(void)
 static int HTPCallbackRequest(htp_tx_t *tx) {
     SCEnter();
 
+    if (tx == NULL) {
+        SCReturnInt(HTP_ERROR);
+    }
+
     HtpState *hstate = htp_connp_get_user_data(tx->connp);
     if (hstate == NULL) {
         SCReturnInt(HTP_ERROR);
@@ -1967,7 +1971,6 @@ static int HTPCallbackRequest(htp_tx_t *tx) {
 
     SCLogDebug("HTTP request completed");
 
-    if (tx != NULL) {
     HTPErrorCheckTxRequestFlags(hstate, tx);
 
     HtpTxUserData *htud = (HtpTxUserData *)htp_tx_get_user_data(tx);
@@ -1978,7 +1981,6 @@ static int HTPCallbackRequest(htp_tx_t *tx) {
             htud->tsflags &= ~HTP_FILENAME_SET;
         }
     }
-    }
 
     /* request done, do raw reassembly now to inspect state and stream
      * at the same time. */