### Godot version

4.1.1

### System information

linux

### Issue description

The `"%+f"` format adds a `+` sign in front of positive numbers. If you try to format `-0.0`, it breaks and displays both a `+` and a `-`.

### Steps to reproduce

```gdscript
@tool
extends EditorScript

func _run() -> void:
    print("%+f" % -0.0)
```

### Minimal reproduction project

see above
} else if (value > 0x10ffff) {
							return "unsigned integer is greater than maximum";
						}
						str = chr(values[value_index]);
					} else if (values[value_index].get_type() == Variant::STRING) {
						str = values[value_index];
						if (str.length() != 1) {
							return "%c requires number or single-character string";
						}
					} else {
						return "%c requires number or single-character string";
					}
					// 
					if (left_justified) {
						str = str.rpad(min_chars);
					} else {
						str = str.lpad(min_chars);
					}
					formatted += str;
					++value_index;
					in_format = false;
					break;
				}
				case '-': { // 
					left_justified = true;
					break;
				}
				case '+': { // 
					show_sign = true;
					break;