[GDNative] Godot::print and String() randomly change the input char*

Both the `Godot::print(const char*)` and `String(const char*)`-methods randomly change the content of their input `const char*`.

Here's a minimal reproduction method:

```cpp
void SQLite::test(String input)
{
const CharString dummy_input = input.utf8();
const char *char_input = dummy_input.get_data();

std::cout << char_input << std::endl;

Godot::print(char_input);

std::cout << char_input << std::endl;
}
```

Code in Godot itself:
```gdscript
func _ready() -> void:
db = SQLite.new()
db.test("I love GDNative!")
```

Which prints in the console:
```
I love GDNative!
I love GDNative!
I love GDNative!
```
or
```
I love GDNative!
I love GDNative!
I
```
or
```
I love GDNative!
I love GDNative!
▐↕▬
```
or other similar random junk

Why is this happening? Am I not allowed to use char_input anymore after I print it?