libwebp: update snapshot to v0.3.0-rc6

third_party/libwebp/utils/utils.c

Index: third_party/libwebp/utils/utils.c
diff --git a/third_party/libwebp/utils/utils.c b/third_party/libwebp/utils/utils.c
index 673b7e284c3d0c8563dcfb315d6c4fccacf8754f..b1db2f9d6d53df36453d3f76403b6826fa3abd9b 100644
--- a/third_party/libwebp/utils/utils.c
+++ b/third_party/libwebp/utils/utils.c
@@ -19,7 +19,8 @@ extern "C" {
 //------------------------------------------------------------------------------
 // Checked memory allocation
 
-static int CheckSizeArguments(uint64_t nmemb, size_t size) {
+// Returns 0 in case of overflow of nmemb * size.
+static int CheckSizeArgumentsOverflow(uint64_t nmemb, size_t size) {
   const uint64_t total_size = nmemb * size;
   if (nmemb == 0) return 1;
   if ((uint64_t)size > WEBP_MAX_ALLOCABLE_MEMORY / nmemb) return 0;
@@ -28,12 +29,14 @@ static int CheckSizeArguments(uint64_t nmemb, size_t size) {
 }
 
 void* WebPSafeMalloc(uint64_t nmemb, size_t size) {
-  if (!CheckSizeArguments(nmemb, size)) return NULL;
+  if (!CheckSizeArgumentsOverflow(nmemb, size)) return NULL;
+  assert(nmemb * size > 0);
   return malloc((size_t)(nmemb * size));
 }
 
 void* WebPSafeCalloc(uint64_t nmemb, size_t size) {
-  if (!CheckSizeArguments(nmemb, size)) return NULL;
+  if (!CheckSizeArgumentsOverflow(nmemb, size)) return NULL;
+  assert(nmemb * size > 0);
   return calloc((size_t)nmemb, size);
 }