Catch integer overflows/underflows when parsing corrupt DWARF FORM blocks.

	PR 22895
	PR 22893
	* dwarf2.c (read_n_bytes): Replace size parameter with dwarf_block
	pointer.  Drop unused abfd parameter.  Check the size of the block
	before initialising the data field.  Return the end pointer if the
	size is invalid.
	(read_attribute_value): Adjust invocations of read_n_bytes.