fdo#62088: Fix crash on master page switch too.

This is actually a regression caused by
1165aac9, where a confusing code was removed,
that should have stayed there.

Re-introduced in a readable way.

Change-Id: Ib99c19c04cf3b098097cef8da5da63b8cc7dd130

svx/source/form/fmpgeimp.cxx

@@ -162,6 +162,9 @@ void FmFormPageImpl::initFrom( FmFormPageImpl& i_foreignImpl )
     // clone the Forms collection
     const Reference< css::form::XForms > xForeignForms( const_cast< FmFormPageImpl& >( i_foreignImpl ).getForms( false ) );
 
+    if ( !xForeignForms.is() )
+        return;
+
     try
     {
         m_xForms.set( xForeignForms->createClone(), UNO_QUERY_THROW );