threads/lib: fix coverity check for unchecked return code

In thread startup, return error of TmThreadsWaitForUnpause() fails.
Fixed coverity check as in all other places the return value of this
function is checked and acted on.

src/tm-threads.c

@@ -396,13 +396,15 @@ static void *TmThreadsLib(void *td)
         goto error;
     }
 
-    TmThreadsWaitForUnpause(tv);
+    if (!TmThreadsWaitForUnpause(tv)) {
+        goto error;
+    }
 
     return NULL;
 
 error:
     tv->stream_pq = NULL;
-    return NULL;
+    return (void *)-1;
 }
 
 static void *TmThreadsSlotVar(void *td)
@@ -1751,7 +1753,9 @@ TmEcode TmThreadLibSpawn(ThreadVars *tv)
         return TM_ECODE_FAILED;
     }
 
-    tv->tm_func((void *)tv);
+    if (tv->tm_func((void *)tv) == (void *)-1) {
+        return TM_ECODE_FAILED;
+    }
 
     TmThreadWaitForFlag(tv, THV_INIT_DONE | THV_RUNNING_DONE);