Bug #22131713 QUERYING STATUS_BY_USER/HOST/ACCOUNT CAUSES THE MYSQL SERVER TO CRASH

Issue:
------
    While aggregating stats for user/host/account a null check was missing
    to make sure account stats exist. In specific case reported here, stats
    for account were not supposed to be collected as specified by user
    therefore absense of this NULL check was causing crash.

Fix:
----
    Addded a NULL check before dereferencing account stats pointer.

Author: mayprasa

storage/perfschema/pfs_visitor.cc

@@ -132,9 +132,12 @@ class All_host_THD_visitor_adapter : public Do_THD_Impl
     if (pfs != NULL)
     {
       PFS_account *account= sanitize_account(pfs->m_account);
-      if (account->m_host == m_host)
+      if (account != NULL)
       {
-        m_visitor->visit_THD(thd);
+        if (account->m_host == m_host)
+        {
+          m_visitor->visit_THD(thd);
+        }
       }
       else if (pfs->m_host == m_host)
       {
@@ -218,9 +221,12 @@ class All_user_THD_visitor_adapter : public Do_THD_Impl
     if (pfs != NULL)
     {
       PFS_account *account= sanitize_account(pfs->m_account);
-      if (account->m_user == m_user)
+      if (account != NULL)
       {
-        m_visitor->visit_THD(thd);
+        if (account->m_user == m_user)
+        {
+          m_visitor->visit_THD(thd);
+        }
       }
       else if (pfs->m_user == m_user)
       {