[xsl] Find a specific element or fall back to element 1

I have a gallery.xml file containing a number of images:

<gallery>
    <image>
      <filename>1.jpg</filename>
    </image>
    <image>
      <filename>2.jpg</filename>
    </image>
    <!-- etc -->
    <image default="true">
      <!-- optional attribute applies to this element -->
      <filename>10.jpg</filename>
    </image>
</gallery>

and my xslt has to do the following thing -- look for an image marked
with a "default" attribute, and if it's not found, use the first image
instead. So I'm looking for the position number of the marked element,
and if I can't find it, using 1:

<xsl:variable name="gallery-xml-file"
select="document($gallery-xml-path)"/>
<xsl:variable name="test-position">
  <xsl:for-each select="$gallery-xml-file//image">
    <xsl:if test="@default='true'">
      <xsl:value-of select="position()"/>
    </xsl:if>
  </xsl:for-each>
</xsl:variable>
<xsl:variable name="display-position">
  <xsl:choose>
    <xsl:when test="$test-position = ''">1</xsl:when>
    <xsl:otherwise>
      <xsl:value-of select="$test-position"/>
    </xsl:otherwise>
  </xsl:choose>
</xsl:variable>

This seems a bit long and wasteful to me. Is there a better way?

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