Fail when TLS context fails to initialise

+  log_info(LD_GENERAL,"Rotating tls context.");
+  if (router_initialize_tls_context() < 0) {
+    log_warn(LD_BUG, "Error reinitializing TLS context");
+    /* XXX is it a bug here, that we just keep going? -RD */
   }

I think it is - how about we assert() here, and see what happens?