[Ada] Do not create large objects for indefinite protected types

[Ada] Do not create large objects for indefinite protected types

This plugs a small loophole in the Needs_Secondary_Stack predicate for
some protected types and record types containing protected components.

gcc/ada/

	* sem_util.adb (Caller_Known_Size_Record): Make entry assertion
	more robust and add guard for null argument.  For protected
	types, invoke Caller_Known_Size_Record on
	Corresponding_Record_Type.
	(Needs_Secondary_Stack): Likewise.