Close resource leaks in the BFD library's plugin handler.

Close resource leaks in the BFD library's plugin handler.

	PR 23460
	* plugin.c (bfd_plugin_open_input): Close file descriptor if the
	call to fstat fails.
	(try_claim): Always close the file descriptor at the end of the
	function.
	(try_load_plugin): If a plugin has already been registered, then
	skip the dlopen and onload steps and go straight to claiming the
	file.  If these is an error, close the plugin.