Doxygen comment parsing fix for empty lines in code/verbatim blocks

Fix how end of paragraph is identified when parsing \code and
\verbatim blocks that appear within a paragraph and contain an empty
line.  Previously this would generate a warning for unexpected end of
doxygen comments, and it could generate a segfault due to
dereferencing an invalid iterator value.

The doxygen_basic_translate.i and doxygen_basic_translate_style2.i
tests have been updated to serve as regression tests for this
behavior.  Prior to this fix, inclusion of the empty code block line
in this context produced a segfault.

Examples/test-suite/doxygen_basic_translate_style2.i

@@ -55,6 +55,8 @@ void function3(int a, int b)
  *  \warning This may not work as expected
  *  \code
  *  int main() { while(true); }
+ *
+ *  // Test blank line in code block
  *  \endcode
  *  \endif
  */