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

core/src/fxcrt/fxcrt_posix.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 "fxcrt_posix.h"
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_LINUX_ || _FXM_PLATFORM_ == _FXM_PLATFORM_APPLE_ || _FXM_PLATFORM_ == _FXM_PLATFORM_ANDROID_
 IFXCRT_FileAccess* FXCRT_FileAccess_Create()
@@ skipping 147 matching lines @@
     }
     FX_FILESIZE size = src.GetSize();
     if (!size) {
         return FALSE;
     }
     if (!dst.Open(fileNameDst, FX_FILEMODE_Truncate)) {
         return FALSE;
     }
     size_t num = 0;
     FX_LPBYTE pBuffer = FX_Alloc(FX_BYTE, 32768);
+    if (!pBuffer) {
+        return FALSE;
+    }
     num = src.Read(pBuffer, 32768);
     while (num) {
         if (dst.Write(pBuffer, num) != num) {
             break;
         }
         num = src.Read(pBuffer, 32768);
     }
     FX_Free(pBuffer);
     return TRUE;
 }
 FX_BOOL FX_File_Copy(FX_WSTR fileNameSrc, FX_WSTR fileNameDst)
 {
     return FX_File_Copy(FX_UTF8Encode(fileNameSrc), FX_UTF8Encode(fileNameDst));
 }
 FX_BOOL FX_File_Move(FX_BSTR fileNameSrc, FX_BSTR fileNameDst)
 {
     return rename(fileNameSrc.GetCStr(), fileNameDst.GetCStr());
 }
 FX_BOOL FX_File_Move(FX_WSTR fileNameSrc, FX_WSTR fileNameDst)
 {
     return FX_File_Move(FX_UTF8Encode(fileNameSrc), FX_UTF8Encode(fileNameDst));
 }
 #endif