Changed code to handle potential empty string.

[seanswyi]

There are certain cases where the colspan attribute is mapped to an empty string and thus causes ValueErrors when trying to cast them to integers.

For example here:

<table>
    <colgroup>
        <col style="width:25%;">
        <col style="width:25%;">
        <col style="width:25%;">
        <col style="width:25%;">
    </colgroup>
    <thead>
        <tr>
            <th rowspan="2" scope="col">Category</th>
            <th rowspan="2" scope="col">Regular Price (per person)</th>
            <th colspan="" scope="col">Online Discounted Price</th>
            <th colspan="" scope="col">On-site Discount Price</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>Adult</td>
            <td>₩69,000</td>
            <td class="cPurple fBold">₩33,100</td>
            <td class="cPurple fBold">₩32,500</td>
        </tr>
        <tr>
            <td>Teenager</td>
            <td>₩61,000</td>
            <td class="cPurple fBold">₩33,100</td>
            <td class="cPurple fBold">₩32,500</td>
        </tr>
        <tr>
            <td>Child</td>
            <td>₩53,000</td>
            <td class="cPurple fBold">₩33,100</td>
            <td class="cPurple fBold">₩32,500</td>
        </tr>
    </tbody>
</table>

The extra line that I added essentially checks to make sure that the result of td.get("colspan") is not an empty string, and if it is then make it default to 1.