Fixes a warning treated as an error for GCC 13 (#138)

- For building Dive with GCC 13 in Release mode, a warning in `snprintf`
  treated as an error is produced.
- Adding an extra byte for null terminator in `snprintf` fixes the warning.

ui/hover_help_model.cpp

@@ -73,7 +73,7 @@ void HoverHelp::SetCurItem(Item        item,
     ;
 #define CASE(index, ...)                                        \
     case Item::index:                                           \
-        cur_string_size = snprintf(NULL, 0, __VA_ARGS__);       \
+        cur_string_size = snprintf(NULL, 0, __VA_ARGS__) + 1;   \
         cur_string.resize(cur_string_size);                     \
         snprintf(&cur_string[0], cur_string_size, __VA_ARGS__); \
         break;