snapshot/mac: MachOImageAnnotationsReader test shouldn’t crash with a nullptr ProcessReader::Module

snapshot/mac/process_reader.h

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 66 matching lines @@
     Module();
     ~Module();
 
     //! \brief The pathname used to load the module from disk.
     std::string name;
 
     //! \brief An image reader for the module.
     //!
     //! The lifetime of this MachOImageReader is scoped to the lifetime of the
     //! ProcessReader that created it.
+    //!
+    //! This field may be `nullptr` if a reader could not be created for the
+    //! module.
     const MachOImageReader* reader;
 
     //! \brief The module’s timestamp.
     //!
     //! This field will be `0` if its value cannot be determined. It can only be
     //! determined for images that are loaded by dyld, so it will be `0` for the
     //! main executable and for dyld itself.
     time_t timestamp;
   };
 
@@ skipping 130 matching lines @@
 
   bool initialized_threads_;
   bool initialized_modules_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessReader);
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_SNAPSHOT_MAC_PROCESS_READER_H_