Unmap the buffer if plugin didn't claim the file

Unmap the buffer if plugin didn't claim the file

If plugin didn't claim the file, unmap the buffer.

	* plugin.c (plugin_input_file_t): Add use_mmap.
	(plugin_pagesize): New.
	(get_view): Use plugin_pagesize.  Set use_mmap if mmap is used.
	(plugin_load_plugins): Initialize plugin_pagesize.
	(plugin_maybe_claim): Unmap the buffer if plugin didn't claim the
	file.