Including the same image multiple times at different sizes replaces the first image tag

If intentionally inserting the same image multiple times into the same post, there is a chance that Image Resize Filter will replace the "src" attribute of the wrong tag.

For example posting something like this:

<strong>Not resized: </strong>
<img src="http://drupal6/files/lullabot.png" width="65" height="80" />

<strong>Resized: </strong>
<img src="http://drupal6/files/lullabot.png" width="10" height="10" />

When viewing the node the HTML comes out like this:

<strong>Not resized: </strong>
<img src="http://drupal6/files/resize/lullabot.png-10x10" width="65" height="80" />

<strong>Resized: </strong>
<img src="http://drupal6/files/lullabot.png" width="10" height="10" />

The first image has been replaced with the 10x10 size version, even though it wasn't resized at all. The second img tag is the one that should have been replaced. This patch should correct this problem.