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/python/doxygen_basic_translate_runme.py

@@ -50,6 +50,8 @@ Warning: This may not work as expected
 .. code-block:: c++
 
     int main() { while(true); }
+
+    // Test blank line in code block
 }"""
 )
 comment_verifier.check(inspect.getdoc(doxygen_basic_translate.function5),

Examples/test-suite/python/doxygen_basic_translate_style2_runme.py

@@ -48,6 +48,8 @@ Warning: This may not work as expected
 .. code-block:: c++
 
     int main() { while(true); }
+
+    // Test blank line in code block
 }"""
 )
 comment_verifier.check(inspect.getdoc(doxygen_basic_translate_style2.function5),