Make sure we open an lvalue of existential type during application.

(cherry picked from commit 6ce2454)

Author: DougGregor

lib/Sema/CSApply.cpp

@@ -5929,7 +5929,8 @@ ArgumentList *ExprRewriter::coerceCallArguments(
 
     // If the argument is an existential type that has been opened, perform
     // the open operation.
-    if (argType->getInOutObjectType()->isAnyExistentialType() &&
+    if (argType->getRValueType()->getInOutObjectType()
+            ->isAnyExistentialType() &&
         paramType->hasOpenedExistential()) {
       // FIXME: Look for an opened existential and use it. We need to
       // know how far out we need to go to close the existentials. Huh.