Fix potential out-of-bounds in next_split_s() wrt buffer length

next_split_s() could potentially commit out-of-bounds indexing if the
amount of source data was bigger than the destination data.

This is because the size of the source data passed in includes the null
terminator, so if 1 byte is not subtracted from it, then after it passes
through the VVV_min(), it will index 1 past the end of the passed buffer
when null-terminating it.

In contrast, the other argument of the VVV_min() does not need 1
subtracted from it, because that length does not include a null
terminator (next_split() returns the length of the substring, after all;
not the length of the substring plus 1).

(The VVV_min() here also shortens the range of values to the size of an
int, but we'll probably make size_t versions anyway; plus who really
cares about supporting massively-sized buffers bigger than 2 billion
bytes in length? That just doesn't make sense.)

desktop_version/src/UtilityClass.cpp

@@ -122,7 +122,7 @@ bool next_split_s(
 		/* Using SDL_strlcpy() here results in calling SDL_strlen() */
 		/* on the whole string, which results in a visible freeze */
 		/* if it's a very large string */
-		const size_t length = VVV_min(buffer_size, len);
+		const size_t length = VVV_min(buffer_size - 1, len);
 		SDL_memcpy(buffer, &str[prev_start], length);
 		buffer[length] = '\0';
 	}