Function stb_textedit_discard_redo

KBotExt/imgui/imstb_textedit.h:1135–1163

discard the oldest entry in the redo list--it's bad if this ever happens, but because undo & redo have to store the actual characters in different cases, the redo character buffer can fill up even though the undo buffer didn't

// characters in different cases, the redo character buffer can
// fill up even though the undo buffer didn't
static void stb_textedit_discard_redo(StbUndoState* state)
{
	int k = STB_TEXTEDIT_UNDOSTATECOUNT - 1;

	if (state->redo_point <= k) {
		// if the k'th undo state has characters, clean those up
		if (state->undo_rec[k].char_storage >= 0) {
			int n = state->undo_rec[k].insert_length, i;
			// move the remaining redo character data to the end of the buffer
			state->redo_char_point += n;
			STB_TEXTEDIT_memmove(state->undo_char + state->redo_char_point, state->undo_char + state->redo_char_point - n, (size_t)((STB_TEXTEDIT_UNDOCHARCOUNT - state->redo_char_point) * sizeof(STB_TEXTEDIT_CHARTYPE)));
			// adjust the position of all the other records to account for above memmove
			for (i = state->redo_point; i < k; ++i)
				if (state->undo_rec[i].char_storage >= 0)
					state->undo_rec[i].char_storage += n;
		}
		// now move all the redo records towards the end of the buffer; the first one is at 'redo_point'
		// [DEAR IMGUI]
		size_t move_size = (size_t)((STB_TEXTEDIT_UNDOSTATECOUNT - state->redo_point - 1) * sizeof(state->undo_rec[0]));
		const char* buf_begin = (char*)state->undo_rec; (void)buf_begin;
		const char* buf_end = (char*)state->undo_rec + sizeof(state->undo_rec); (void)buf_end;
		IM_ASSERT(((char*)(state->undo_rec + state->redo_point)) >= buf_begin);
		IM_ASSERT(((char*)(state->undo_rec + state->redo_point + 1) + move_size) <= buf_end);
		STB_TEXTEDIT_memmove(state->undo_rec + state->redo_point + 1, state->undo_rec + state->redo_point, move_size);

		// now move redo_point to point to the new one
		++state->redo_point;
	}
}

static StbUndoRecord* stb_text_create_undo_record(StbUndoState* state, int numchars)
{