[Property wrappers] Fix another opaque-result-types crasher.

Test case from Holly Borla, thank you!

(cherry picked from commit 3e7b4ae)

Author: DougGregor

lib/Sema/TypeCheckStorage.cpp

@@ -2684,16 +2684,17 @@ PropertyWrapperBackingPropertyInfoRequest::evaluate(Evaluator &evaluator,
     pbd->setInit(0, initializer);
     pbd->setInitializerChecked(0);
     wrappedValue = findWrappedValuePlaceholder(initializer);
-  } else if (!parentPBD->isInitialized(patternNumber) &&
-             wrapperInfo.defaultInit) {
-    // FIXME: Record this expression somewhere so that DI can perform the
-    // initialization itself.
-    auto typeExpr = TypeExpr::createImplicit(storageType, ctx);
-    Expr *initializer = CallExpr::createImplicit(ctx, typeExpr, {}, { });
-    typeCheckSynthesizedWrapperInitializer(pbd, backingVar, parentPBD,
-                                           initializer);
-    pbd->setInit(0, initializer);
-    pbd->setInitializerChecked(0);
+  } else {
+    if (!parentPBD->isInitialized(patternNumber) && wrapperInfo.defaultInit) {
+      // FIXME: Record this expression somewhere so that DI can perform the
+      // initialization itself.
+      auto typeExpr = TypeExpr::createImplicit(storageType, ctx);
+      Expr *initializer = CallExpr::createImplicit(ctx, typeExpr, {}, { });
+      typeCheckSynthesizedWrapperInitializer(pbd, backingVar, parentPBD,
+                                             initializer);
+      pbd->setInit(0, initializer);
+      pbd->setInitializerChecked(0);
+    }
 
     if (var->getOpaqueResultTypeDecl()) {
       var->diagnose(diag::opaque_type_var_no_underlying_type);

test/decl/var/property_wrappers_opaque.swift

@@ -22,3 +22,6 @@ struct FB7699647 {
   @WrapperWithDefaultInit() var otherProperty: some P // expected-error{{property declares an opaque return type, but cannot infer the underlying type from its initializer expression}}
 }
 
+struct FB7699647b {
+  @WrapperWithDefaultInit var property: some P // expected-error{{property declares an opaque return type, but cannot infer the underlying type from its initializer expression}}
+}