### 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
for (int i = -nblocks; i; i++) {
		uint32_t k1 = blocks[i];
		k1 *= c1;
		k1 = hash_rotl32(k1, 15);
		k1 *= c2;
		h1 ^= k1;
		h1 = hash_rotl32(h1, 13);
		h1 = h1 * 5 + 0xe6546b64;
	}
	const uint8_t *tail = (const uint8_t *)(data + nblocks * 4);
	uint32_t k1 = 0;
	switch (length & 3) {
		case 3:
			k1 ^= tail[2] << 16;
			[[fallthrough]];
		case 2:
			k1 ^= tail[1] << 8;
			[[fallthrough]];
		case 1:
			k1 ^= tail[0];
			k1 *= c1;
			k1 = hash_rotl32(k1, 15);
			k1 *= c2;
			h1 ^= k1;
	};
	
	h1 ^= length;
	return hash_fmix32(h1);
}
static _FORCE_INLINE_ uint32_t hash_djb2_one_float(double p_in, uint32_t p_prev = 5381) {