### Godot version

4.2.x master [5df98679672c12d96b4ac4d96ee17f1559207401]

### System information

Linux - GCC g++ 9.4.0 - Ubuntu 20.04 LTS

### Issue description

I somehow managed to get my Windows system into a broken state were the driver reports 145 extensions, but extension `#144` is an empty string.

Therefore Godot will crash while initializing Vulkan and looking for requested device extensions.

### Steps to reproduce

Execute the following code:

```cpp
HashMap<CharString, bool> requested_device_extensions;

CharString extension_name("");
CharString extension_name2("Hello");

requested_device_extensions.insert("HashMap must not be empty", true);

if (requested_device_extensions.has(extension_name2))
	printf("Has Hello\n");
if (requested_device_extensions.has(extension_name))
	printf("Has <empty>\n");
```

It will crash before <empty>. Callstack:

                                                                                                                                                                                                
```                                                                                                                                                                                                
1 hash_djb2                                                                                                                                                   hashfuncs.h        64   0x4a135d6 
2 HashMapHasherDefault::hash                                                                                                                                  hashfuncs.h        313  0x4a1decd 
3 HashMap<CharString, bool, HashMapHasherDefault, HashMapComparatorDefault<CharString>, DefaultTypedAllocator<HashMapElement<CharString, bool>>>::_hash       hash_map.h         85   0x4a1dbd9 
4 HashMap<CharString, bool, HashMapHasherDefault, HashMapComparatorDefault<CharString>, DefaultTypedAllocator<HashMapElement<CharString, bool>>>::_lookup_pos hash_map.h         106  0x4a1d8d7 
5 HashMap<CharString, bool, HashMapHasherDefault, HashMapComparatorDefault<CharString>, DefaultTypedAllocator<HashMapElement<CharString, bool>>>::has         hash_map.h         310  0x4a14788 
6 Main::setup                                                                                                                                                 main.cpp           2115 0x4a088d3 
7 main                                                                                                                                                        godot_linuxbsd.cpp 62   0x497f058 
```

The reason is that CharString decided to not create a pointer at all to save memory. Hence when hash_djb2 tries to read the first byte, it crashes.

### Minimal reproduction project

N / A
#ifndef HASHFUNCS_H
#define HASHFUNCS_H
#include "core/math/aabb.h"
#include "core/math/math_defs.h"
#include "core/math/math_funcs.h"
#include "core/math/rect2.h"
#include "core/math/rect2i.h"
#include "core/math/vector2.h"
#include "core/math/vector2i.h"
#include "core/math/vector3.h"
#include "core/math/vector3i.h"
#include "core/math/vector4.h"
#include "core/math/vector4i.h"
#include "core/object/object_id.h"
#include "core/string/node_path.h"
#include "core/string/string_name.h"
#include "core/string/ustring.h"
#include "core/templates/rid.h"
#include "core/typedefs.h"
/**
 * Hashing functions
 */
/**
 * DJB2 Hash function
 * @param C String
 * @return 32-bits hashcode
 */
static _FORCE_INLINE_ uint32_t hash_djb2(const char *p_cstr) {