[CSApply] Mark initializer as checked after it is set

Once coerced initializer expression has been set for
a particular pattern binding entry, let's mark it as
checked, otherwise decl checker might try to
re-typecheck it.

Author: xedin

lib/Sema/CSApply.cpp

@@ -8811,6 +8811,7 @@ ExprWalker::rewriteTarget(SolutionApplicationTarget target) {
 
       if (patternBinding->getInit(index)) {
         patternBinding->setInit(index, resultTarget->getAsExpr());
+        patternBinding->setInitializerChecked(index);
       }
     }