### 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
23987963684927896,
	11955116055547344,
	5991147799191151,
	2998982941588287,
	1501077717772769,
	750081082979285,
	375261795343686,
	187625172388393,
	93822606204624,
	46909513691883,
	23456218233098,
	11728086747027,
	5864041509391,
	2932024948977,
	1466014921160,
	733007198436,
	366503839517,
	183251896093,
	91625960335,
	45812983922,
	22906489714,
	11453246088
};
/**
 * Fastmod computes ( n mod d ) given the precomputed c much faster than n % d.
 * The implementation of fastmod is based on the following paper by Daniel Lemire et al.
 * Faster Remainder by Direct Computation: Applications to Compilers and Software Libraries
 * https://arxiv.org/abs/1902.01961
 */
static _FORCE_INLINE_ uint32_t fastmod(const uint32_t n, const uint64_t c, const uint32_t d) {