internal/filedesc: fix parsing of enforce_utf8 option

Remove spurious negation.

Change-Id: I484fa6fecda85943cdedd96a6c6f0f2349f6bfee
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/188338
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/internal/filedesc/desc_lazy.go b/internal/filedesc/desc_lazy.go
index 9b54e6d..9e2b21c 100644
--- a/internal/filedesc/desc_lazy.go
+++ b/internal/filedesc/desc_lazy.go
@@ -497,7 +497,7 @@
 				fd.L1.IsWeak = wire.DecodeBool(v)
 			case FieldOptions_EnforceUTF8:
 				fd.L1.HasEnforceUTF8 = true
-				fd.L1.EnforceUTF8 = !wire.DecodeBool(v)
+				fd.L1.EnforceUTF8 = wire.DecodeBool(v)
 			}
 		default:
 			m := wire.ConsumeFieldValue(num, typ, b)