Cleanup handling of quantified expressions before using it as an inspiration
for fixing the handling of iterated component associations. Behavior is
unaffected.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_ch4.adb
	(Is_Empty_Range): Move error reporting to the caller.
	(Analyze_Qualified_Expression): Move error reporting from Is_Empty_Range;
	add matching call to End_Scope before rewriting and returning.