Fix a vicious bug in symbol table management

Functions identifiers are also stored in symbol tables.
When a block of code is left, all local variables are reset to avoid
useless memory consumption.

The problem was that locally defined functions lost their associate id
which is necessary to retrieve the function in the function
table. When a function was defined in a block, its id were set to 0...

Now functions identifiers are no more clean-up.

src/language/utils/SymbolTable.hpp

@@ -267,6 +267,8 @@ class SymbolTable
   clearValues()
   {
     for (auto& symbol : m_symbol_list) {
+      // local functions must kept their values (id)
+      if (symbol.attributes().dataType() != ASTNodeDataType::function_t) {
         std::visit(
           [](auto&& value) {
             using T = std::decay_t<decltype(value)>;
@@ -275,6 +277,7 @@ class SymbolTable
           symbol.attributes().value());
       }
     }
+  }
 
   auto
   find(const std::string& symbol, const TAO_PEGTL_NAMESPACE::position& use_position)