ubsan: Don’t call v[0] on empty vectors

snapshot/minidump/process_snapshot_minidump.cc

 // Copyright 2015 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 47 matching lines @@
   if (header_.Version != MINIDUMP_VERSION) {
     LOG(ERROR) << "minidump version mismatch";
     return false;
   }
 
   if (!file_reader->SeekSet(header_.StreamDirectoryRva)) {
     return false;
   }
 
   stream_directory_.resize(header_.NumberOfStreams);
-  if (!file_reader_->ReadExactly(
+  if (!stream_directory_.empty() &&
+      !file_reader_->ReadExactly(
           &stream_directory_[0],
           header_.NumberOfStreams * sizeof(stream_directory_[0]))) {
     return false;
   }
 
   for (const MINIDUMP_DIRECTORY& directory : stream_directory_) {
     const MinidumpStreamType stream_type =
         static_cast<MinidumpStreamType>(directory.StreamType);
     if (stream_map_.find(stream_type) != stream_map_.end()) {
       LOG(ERROR) << "duplicate streams for type " << directory.StreamType;
@@ skipping 237 matching lines @@
           << "duplicate module_crashpad_info_list minidump_module_list_index "
           << minidump_link.minidump_module_list_index;
       return false;
     }
   }
 
   return true;
 }
 
 }  // namespace crashpad