Update libwebp to 0.4.0

third_party/libwebp/utils/bit_writer.c

Index: third_party/libwebp/utils/bit_writer.c
diff --git a/third_party/libwebp/utils/bit_writer.c b/third_party/libwebp/utils/bit_writer.c
index 3827a13ad1efe7be95808c7b5510a2838aafa30b..29810a17492fa4a53a0809ae5959a207a6246747 100644
--- a/third_party/libwebp/utils/bit_writer.c
+++ b/third_party/libwebp/utils/bit_writer.c
@@ -17,10 +17,6 @@
 #include <stdlib.h>
 #include "./bit_writer.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 //------------------------------------------------------------------------------
 // VP8BitWriter
 
@@ -43,7 +39,10 @@ static int BitWriterResize(VP8BitWriter* const bw, size_t extra_size) {
     bw->error_ = 1;
     return 0;
   }
-  memcpy(new_buf, bw->buf_, bw->pos_);
+  if (bw->pos_ > 0) {
+    assert(bw->buf_ != NULL);
+    memcpy(new_buf, bw->buf_, bw->pos_);
+  }
   free(bw->buf_);
   bw->buf_ = new_buf;
   bw->max_pos_ = new_size;
@@ -253,7 +252,7 @@ void VP8LWriteBits(VP8LBitWriter* const bw, int n_bits, uint32_t bits) {
     uint8_t* p = &bw->buf_[bw->bit_pos_ >> 3];
     const int bits_reserved_in_first_byte = bw->bit_pos_ & 7;
     const int bits_left_to_write = n_bits - 8 + bits_reserved_in_first_byte;
-    // implicit & 0xff is assumed for uint8_t arithmetics
+    // implicit & 0xff is assumed for uint8_t arithmetic
     *p++ |= bits << bits_reserved_in_first_byte;
     bits >>= 8 - bits_reserved_in_first_byte;
     if (bits_left_to_write >= 1) {
@@ -281,6 +280,3 @@ void VP8LWriteBits(VP8LBitWriter* const bw, int n_bits, uint32_t bits) {
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif