Use bfd_map_over_sections to walk section chain.

Do not dump the contents of an empty section.

binutils/doc/binutils.texi

@@ -1481,7 +1481,7 @@ object files.
 
 The long and short forms of options, shown here as alternatives, are
 equivalent.  At least one option from the list
-@option{-a,-d,-D,-e,-f,-g,-G,-h,-H,-p,-r,-R,-S,-t,-T,-V,-x} must be given.
+@option{-a,-d,-D,-e,-f,-g,-G,-h,-H,-p,-r,-R,-s,-S,-t,-T,-V,-x} must be given.
 
 @table @env
 @item -a
@@ -1738,7 +1738,8 @@ libraries.
 @itemx --full-contents
 @cindex sections, full contents
 @cindex object file sections
-Display the full contents of any sections requested.
+Display the full contents of any sections requested.  By default all
+non-empty sections are displayed.
 
 @item -S
 @itemx --source