Fix to VHDL scanner.

The following code should produce two groups, each containing one page, within the same documentation scope,
currently it nests these groups and pages, resulting in incorrect documentation.

--! \defgroup group1 Group 1
--! \{
--!   @brief Group 1
--! \}

--! \ingroup group1
--! \{
--! \page group1_page1 Page 1
--! \verbatim
--!  Some Page 1 text
--! \endverbatim
--! \}

--! \defgroup group2 Group 2
--! \{
--!   @brief Group 2
--! \}

--! \ingroup group2
--! \{
--! \page group2_page1 Page 1
--! \verbatim
--!  Some Page 1 text
--! \endverbatim
--! \}

Similar C code to demonstrate the correct output.

//! \defgroup group1 Group 1
//! \{
//!   @brief Group 1
//! \}

//! \ingroup group1
//! \{
//! \page group1_page1 Page 1
//! \verbatim
//!  Some Page 1 text
//! \endverbatim
//! \}

//! \defgroup group2 Group 2
//! \{
//!   @brief Group 2
//! \}

//! \ingroup group2
//! \{
//! \page group2_page1 Page 1
//! \verbatim
//!  Some Page 1 text
//! \endverbatim
//! \}

Looks like the VHDL scanner is currently ignoring all blank lines between doxygen comment blocks, it probably shouldn't.