[Fix](Olap)Fixs uninitialized group_data_size in CompactionSampleInfo (#57523)

Fixs the uninitialized `group_data_size` in CompactionSampleInfo, which
resulted in an unreasonable `batch_size` for the estimate_batch_size()
method.

Author: uchenily

be/src/olap/iterators.h

@@ -156,7 +156,7 @@ class StorageReadOptions {
 struct CompactionSampleInfo {
     int64_t bytes = 0;
     int64_t rows = 0;
-    int64_t group_data_size;
+    int64_t group_data_size = 0;
 };
 
 struct BlockWithSameBit {

be/src/olap/merger.cpp

@@ -477,7 +477,7 @@ Status Merger::vertical_merge_rowsets(BaseTabletSPtr tablet, ReaderType reader_t
             tablet->tablet_id(), dst_rowset_writer->context().tablet_path, reader_type);
     {
         std::unique_lock<std::mutex> lock(tablet->sample_info_lock);
-        tablet->sample_infos.resize(column_groups.size(), {0, 0, 0});
+        tablet->sample_infos.resize(column_groups.size());
     }
     // compact group one by one
     for (auto i = 0; i < column_groups.size(); ++i) {