MDEV-20505: Server crash on startup beacuse of bad wsrep configuration

Problem was that if user used bad wsrep configuration
we call unireg_abort and in wsrep case there is check
to wsrep_server_state that might not yet be initialized.
Fixed by checking that wsrep_server_state is initialized
before checking it's state.

Changes to be committed:
	modified:   sql/mysqld.cc
	modified:   sql/wsrep_server_state.h

sql/mysqld.cc

@@ -1879,6 +1879,7 @@ extern "C" void unireg_abort(int exit_code)
 
 #ifdef WITH_WSREP
   if (WSREP_ON &&
+      Wsrep_server_state::is_inited() &&
       Wsrep_server_state::instance().state() != wsrep::server_state::s_disconnected)
   {
     /*
@@ -5108,6 +5109,7 @@ static int init_server_components()
 
 #ifdef WITH_WSREP
   if (wsrep_init_server()) unireg_abort(1);
+
   if (WSREP_ON && !wsrep_recovery && !opt_abort)
   {
     if (opt_bootstrap) // bootsrap option given - disable wsrep functionality

sql/wsrep_server_state.h

@@ -35,11 +35,17 @@ class Wsrep_server_state : public wsrep::server_state
                         const wsrep::gtid& initial_position,
                         int max_protocol_version);
   static void destroy();
+
   static Wsrep_server_state& instance()
   {
     return *m_instance;
   }
 
+  static bool is_inited()
+  {
+    return (m_instance != NULL);
+  }
+
   static wsrep::provider& get_provider()
   {
     return instance().provider();