internal/impl: fix reversed IsValid test

Change-Id: Iaf5291a6bf31ad3dd130fca06840cec66b896f59
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/211558
Reviewed-by: Joe Tsai <joetsai@google.com>
diff --git a/internal/impl/message_reflect_gen.go b/internal/impl/message_reflect_gen.go
index e894659..94bc88c 100644
--- a/internal/impl/message_reflect_gen.go
+++ b/internal/impl/message_reflect_gen.go
@@ -125,7 +125,7 @@
 	m.messageInfo().setUnknown(m.pointer(), b)
 }
 func (m *messageState) IsValid() bool {
-	return m.pointer().IsNil()
+	return !m.pointer().IsNil()
 }
 
 func (m *messageReflectWrapper) Descriptor() protoreflect.MessageDescriptor {
@@ -245,5 +245,5 @@
 	m.messageInfo().setUnknown(m.pointer(), b)
 }
 func (m *messageReflectWrapper) IsValid() bool {
-	return m.pointer().IsNil()
+	return !m.pointer().IsNil()
 }