[Core] Fix crash when hashing empty `CharString`

(cherry picked from commit ca5ec6aec1b77b5200e0c728518a9be89b72cfcd)

core/templates/hashfuncs.h

@@ -310,7 +310,7 @@ struct HashMapHasherDefault {
 	static _FORCE_INLINE_ uint32_t hash(const char16_t p_uchar) { return hash_fmix32(p_uchar); }
 	static _FORCE_INLINE_ uint32_t hash(const char32_t p_uchar) { return hash_fmix32(p_uchar); }
 	static _FORCE_INLINE_ uint32_t hash(const RID &p_rid) { return hash_one_uint64(p_rid.get_id()); }
-	static _FORCE_INLINE_ uint32_t hash(const CharString &p_char_string) { return hash_djb2(p_char_string.ptr()); }
+	static _FORCE_INLINE_ uint32_t hash(const CharString &p_char_string) { return hash_djb2(p_char_string.get_data()); }
 	static _FORCE_INLINE_ uint32_t hash(const StringName &p_string_name) { return p_string_name.hash(); }
 	static _FORCE_INLINE_ uint32_t hash(const NodePath &p_path) { return p_path.hash(); }
 	static _FORCE_INLINE_ uint32_t hash(const ObjectID &p_id) { return hash_one_uint64(p_id); }