fix a memory leak in sysvars

GET_STR_ALLOC options are allocated by my_getopt in init_one_value().

but maria-backup never calls handle_option() for them at all,
so Sys_var_charptr_base needs a protection for partially-initialized
variables.

followup for f33367f

Author: vuvova

sql/sys_vars.inl

@@ -520,14 +520,11 @@ public:
      (think of an exit because of an error right after my_getopt)
     */
     option.var_type|= (flags & ALLOCATED) ? GET_STR_ALLOC : GET_STR;
-    if (def_val && (flags & ALLOCATED))
-      global_var(const char*)= my_strdup(PSI_INSTRUMENT_ME, def_val, MYF(0));
-    else
-      global_var(const char*)= def_val;
+    global_var(const char*)= def_val;
   }
   void cleanup() override
   {
-    if (flags & ALLOCATED)
+    if (flags & ALLOCATED && global_var(intptr) != (intptr)option.def_value)
     {
       my_free(global_var(char*));
       global_var(char *)= NULL;
@@ -583,8 +580,7 @@ public:
   }
   void global_update_finish(char *new_val)
   {
-    if (flags & ALLOCATED)
-      my_free(global_var(char*));
+    cleanup();
     flags|= ALLOCATED;
     global_var(char*)= new_val;
   }

sql/wsrep_var.cc

@@ -33,15 +33,6 @@ ulong   wsrep_reject_queries;
 
 int wsrep_init_vars()
 {
-  my_free((char*) wsrep_provider);
-  my_free((char*) wsrep_provider_options);
-  my_free((char*) wsrep_cluster_address);
-  my_free((char*) wsrep_cluster_name);
-  my_free((char*) wsrep_node_name);
-  my_free((char*) wsrep_node_address);
-  my_free((char*) wsrep_node_incoming_address);
-  my_free((char*) wsrep_start_position);
-
   wsrep_provider        = my_strdup(PSI_INSTRUMENT_ME, WSREP_NONE, MYF(MY_WME));
   wsrep_provider_options= my_strdup(PSI_INSTRUMENT_ME, "", MYF(MY_WME));
   wsrep_cluster_address = my_strdup(PSI_INSTRUMENT_ME, "", MYF(MY_WME));