ada: Apply range checks to preanalyzed aggregate expressions

ada: Apply range checks to preanalyzed aggregate expressions

When preanalyzing expressions in GNATprove mode, e.g. Pre/Post
contracts, we apply checks, because these expressions will never
be expanded. This didn't happen for aggregate expressions, most
likely because of an oversight.

gcc/ada/

	* sem_util.adb (Aggregate_Constraint_Checks): Don't exit early
	when preanalysing in GNATprove mode. Now the condition is
	consistent with other similar conditions in other code.