tdf#137745: crash, when deleting tables and changed relationship isn't changed

bt here:
https://bugs.documentfoundation.org/attachment.cgi?id=166782

some explanations here:
https://bugs.documentfoundation.org/show_bug.cgi?id=137745#c8

Change-Id: I1d9dc8d2e3ad7e3e36c4687cb9b2c5990f2d2c8d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/106715
Tested-by: Jenkins
Reviewed-by: Lionel Mamane <lionel@mamane.lu>

connectivity/source/commontools/TTableHelper.cxx

@@ -72,6 +72,11 @@ public:
     }
     virtual void SAL_CALL elementRemoved( const css::container::ContainerEvent& Event ) override
     {
+        // tdf#137745, perhaps connectivity::OTableHelper::disposing() has been called
+        // which called OTableContainerListener::clear(), so m_pComponent may be null
+        if (m_pComponent == nullptr)
+            return;
+
         OUString sName;
         Event.Accessor  >>= sName;
         if ( m_aRefNames.find(sName) != m_aRefNames.end() )