Fix potential illegal memory access when disassembling corrupt RX binaries.

Fix potential illegal memory access when disassembling corrupt RX binaries.

opcodes * rx-dis.c (get_register_name): New function.  Provides safe
	access to name array.
	(get_condition_name, get_flag_name, get_double_register_name)
	(get_double_register_high_name, get_double_register_low_name)
	(get_double_control_register_name, get_double_condition_name):
	Likewise.
	(print_insn_rx): Use the accessor functions.