multi-detect: error on start if no selector registered

Force user to select the method at startup.

src/detect-engine.c

@@ -1998,6 +1998,12 @@ static DetectEngineThreadCtx *DetectEngineThreadCtxInitForMT(ThreadVars *tv)
     DetectEngineCtx *list = master->list;
     DetectEngineThreadCtx **tenant_det_ctxs = NULL;
 
+    if (master->tenant_selector == TENANT_SELECTOR_UNKNOWN) {
+        SCLogError(SC_ERR_MT_NO_SELECTOR, "no tenant selector set: "
+                                          "set using multi-detect.selector");
+        return NULL;
+    }
+
     while (list) {
         if (list->tenant_id > max_tenant_id)
             max_tenant_id = list->tenant_id;

src/util-error.c

@@ -307,6 +307,7 @@ const char * SCErrorToString(SCError err)
         CASE_CODE (SC_ERR_NETMAP_CREATE);
         CASE_CODE (SC_ERR_NETMAP_READ);
         CASE_CODE (SC_ERR_IPPAIR_INIT);
+        CASE_CODE (SC_ERR_MT_NO_SELECTOR);
     }
 
     return "UNKNOWN_ERROR";

src/util-error.h

@@ -296,6 +296,7 @@ typedef enum {
     SC_ERR_NETMAP_READ,
     SC_ERR_THREAD_DEINIT, /**< thread's deinit function failed */
     SC_ERR_IPPAIR_INIT,
+    SC_ERR_MT_NO_SELECTOR,
 } SCError;
 
 const char *SCErrorToString(SCError);