libwebp: update to 0.4.2-rc2

third_party/libwebp/enc/config.c

Index: third_party/libwebp/enc/config.c
diff --git a/third_party/libwebp/enc/config.c b/third_party/libwebp/enc/config.c
index 4b7aa0f84e82bc2183e854f80e52785bb9d32d9d..53a3bb2e71219a865cd8896c377c9d99d101b3e8 100644
--- a/third_party/libwebp/enc/config.c
+++ b/third_party/libwebp/enc/config.c
@@ -111,7 +111,11 @@ int WebPValidateConfig(const WebPConfig* config) {
     return 0;
   if (config->show_compressed < 0 || config->show_compressed > 1)
     return 0;
+#if WEBP_ENCODER_ABI_VERSION > 0x0204
+  if (config->preprocessing < 0 || config->preprocessing > 7)
+#else
   if (config->preprocessing < 0 || config->preprocessing > 3)
+#endif
     return 0;
   if (config->partitions < 0 || config->partitions > 3)
     return 0;