Uninitialized values of intermediate nodes

If you add values along a multi-level path to the ptree, the values of the intermediate nodes remain uninitialized. The sample code is below
```cpp
#include
#include

enum class NodeType
{
Intermediate,
Root,
Leaf
};

using Tree = boost::property_tree::basic_ptree;

void Print(const Tree& tree, std::string_view name)
{
const auto value = tree.get_value(NodeType::Intermediate);
std::cout << "Name: " << name << ", value: " << static_cast(value) << std::endl;
for (const auto& [childName, subtree]: tree)
Print(subtree, childName);
}

int main() {
Tree tree;
tree.add("Intermediate1.Intermediate2.Leaf", NodeType::Leaf);
tree.put_value(NodeType::Root);
Print(tree, "Root");
}
```
Compiled with boost 1.87 by x86-64 clang-18.1.0
[Godbolt link](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,selection:(endColumn:69,endLineNumber:16,positionColumn:69,positionLineNumber:16,selectionStartColumn:69,selectionStartLineNumber:16,startColumn:69,startLineNumber:16),source:'%23include+%3Cboost/property_tree/ptree.hpp%3E%0A%23include+%3Ciostream%3E%0A%0Aenum+class+NodeType%0A%7B%0A++++Intermediate,%0A++++Root,%0A++++Leaf%0A%7D%3B%0A%0Ausing+Tree+%3D+boost::property_tree::basic_ptree%3Cstd::string,+NodeType%3E%3B%0A%0Avoid+Print(const+Tree%26+tree,+std::string_view+name)%0A%7B%0A++++const+auto+value+%3D+tree.get_value(NodeType::Intermediate)%3B%0A++++std::cout+%3C%3C+%22Name:+%22+%3C%3C+name+%3C%3C+%22,+value:+%22+%3C%3C+static_cast%3Cint%3E(value)+%3C%3C+std::endl%3B%0A++++for+(const+auto%26+%5BchildName,+subtree%5D:+tree)%0A++++++++Print(subtree,+childName)%3B%0A%7D%0A%0Aint+main()+%7B%0A++++Tree+tree%3B%0A++++tree.add(%22Intermediate1.Intermediate2.Leaf%22,+NodeType::Leaf)%3B%0A++++tree.put_value(NodeType::Root)%3B%0A++++Print(tree,+%22Root%22)%3B%0A%7D'),l:'5',n:'0',o:'C%2B%2B+source+%231',t:'0')),k:61.29692832764505,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:executor,i:(argsPanelShown:'1',compilationPanelShown:'0',compiler:clang1810,compilerName:'',compilerOutShown:'0',execArgs:'',execStdin:'',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,libs:!((name:boost,ver:'187'),(name:fmt,ver:'713')),options:'',overrides:!(),runtimeTools:!(),source:1,stdinPanelShown:'1',tree:'1',wrap:'1'),l:'5',n:'0',o:'Executor+x86-64+clang+18.1.0+(C%2B%2B,+Editor+%231)',t:'0')),header:(),k:38.70307167235495,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4)
Possible output:
```
Name: Root, value: 1
Name: Intermediate1, value: 0
Name: Intermediate2, value: -249048016
Name: Leaf, value: 2
```
One of the correction options https://github.com/ilya-talankin/property_tree/pull/1/files

Start by reproducing the reported output with the sample using boost/property_tree/ptree.hpp, then trace the basic_ptree path used by add for intermediate nodes. Compare the intermediate-node values with the explicitly assigned root and leaf values; done means intermediate values are defined and the sample no longer reports indeterminate data.

Written by the indexing model from the issue text.