[BugFix] Fix thrift RuntimeProfile child node number not consistent (…

…backport #54837) (#54865)

Co-authored-by: PengFei Li <[email protected]>

be/src/util/runtime_profile.cpp

@@ -746,13 +746,10 @@ void RuntimeProfile::to_thrift(TRuntimeProfileTree* tree) {
 }
 
 void RuntimeProfile::to_thrift(std::vector<TRuntimeProfileNode>* nodes) {
-    nodes->reserve(nodes->size() + _children.size());
-
     int index = nodes->size();
     nodes->emplace_back();
     TRuntimeProfileNode& node = (*nodes)[index];
     node.name = _name;
-    node.num_children = _children.size();
     node.metadata = _metadata;
     node.indent = true;
 
@@ -810,6 +807,8 @@ void RuntimeProfile::to_thrift(std::vector<TRuntimeProfileNode>* nodes) {
         std::lock_guard<std::mutex> l(_children_lock);
         children = _children;
     }
+    node.num_children = children.size();
+    nodes->reserve(nodes->size() + children.size());
 
     for (auto& i : children) {
         int child_idx = nodes->size();