Avoid reliance on undefined malloc(0) behavior.

AIX returns NULL rather than a valid heap address.

TEST=cctest/test-run-wasm-module/Run_WasmModule_CallAdd_rev
R=titzer@chromium.org, jochen@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/1934633002
Cr-Commit-Position: refs/heads/master@{#35913}

test/cctest/cctest.cc

@@ -136,10 +136,12 @@ static void PrintTestList(CcTest* current) {
 
 class CcTestArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
   virtual void* Allocate(size_t length) {
-    void* data = AllocateUninitialized(length);
+    void* data = AllocateUninitialized(length == 0 ? 1 : length);
     return data == NULL ? data : memset(data, 0, length);
   }
-  virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
+  virtual void* AllocateUninitialized(size_t length) {
+    return malloc(length == 0 ? 1 : length);
+  }
   virtual void Free(void* data, size_t length) { free(data); }
   // TODO(dslomov): Remove when v8:2823 is fixed.
   virtual void Free(void* data) { UNREACHABLE(); }