Assert we don't access htab->stub_group out of range
    
    	2016-03-29  Thomas Preud'homme  <thomas.preudhomme@arm.com>
    
    	bfd/
    	* elf32-arm.c (elf32_arm_get_stub_entry): Assert that we don't access
    	passed the end of htab->stub_group array.
    	(elf32_arm_create_or_find_stub_sec): Likewise.
    	(elf32_arm_create_stub): Likewise.