Revert "Remove FX_Alloc() null checks now that it can't return NULL."

core/src/fxcrt/fx_extension.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "../../include/fxcrt/fx_ext.h"
 #include "extension.h"
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 #include <wincrypt.h>
@@ skipping 257 matching lines @@
 }
 #ifdef __cplusplus
 }
 #endif
 #ifdef __cplusplus
 extern "C" {
 #endif
 FX_LPVOID FX_Random_MT_Start(FX_DWORD dwSeed)
 {
     FX_LPMTRANDOMCONTEXT pContext = FX_Alloc(FX_MTRANDOMCONTEXT, 1);
+    if (!pContext) {
+        return NULL;
+    }
     pContext->mt[0] = dwSeed;
     FX_DWORD &i = pContext->mti;
     FX_LPDWORD pBuf = pContext->mt;
     for (i = 1; i < MT_N; i ++) {
         pBuf[i] = (1812433253UL * (pBuf[i - 1] ^ (pBuf[i - 1] >> 30)) + i);
     }
     pContext->bHaveSeed = TRUE;
     return pContext;
 }
 FX_DWORD FX_Random_MT_Generate(FX_LPVOID pContext)
@@ skipping 85 matching lines @@
 {
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
     FX_GenerateCryptoRandom(pBuffer, iCount);
 #else
     FX_Random_GenerateBase(pBuffer, iCount);
 #endif
 }
 #ifdef __cplusplus
 }
 #endif