Add "block_no_data" parameter for m_IfDataExists tag

I propose to add "block_no_data" parameter for m_IfDataExists tag. Will work the same as for m_RenderElement, so this two will work the same, but less code will be required:

COMMON PART:

<inp2:m_DefineElement name="sample_element">
<inp2:Field name="Name"/>
</inp2:m_DefineElement>

<inp2:m_DefineElement name="no_data">
no data
</inp2:m_DefineElement>

OLD CASE:
<inp2:m_RenderElement name="sample_content" data_exists="1" block_no_data="no_data"/>

NEW CASE:
<inp2:m_IfDataExists block_no_data="no_data">
<inp2:Field name="Name"/>
</inp2:m_IfDataExists>

At the end we have no need to create temporary block to use for data presence check.