xhtml export: Prefer svg if it's available

And not use the replacement graphic in this case.

Change-Id: I5e1bb7a694f210e2681ff5acf241a131d38a4c5d
Reviewed-on: https://gerrit.libreoffice.org/45782Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>
(cherry picked from commit aa768bdb)
Reviewed-on: https://gerrit.libreoffice.org/45801

filter/source/xslt/odf2xhtml/export/xhtml/body.xsl

@@ -1483,10 +1483,12 @@
     <xsl:template match="draw:image | draw:object-ole">
         <xsl:param name="globalData"/>
 
-        <!-- If there is a replacement graphic, we take it.
-             It is a png which browsers are more likely able to render than the original graphic
-             which might have arbitrary formats. -->
-        <xsl:if test="not(following-sibling::draw:image)">
+        <!-- If there is a replacement graphic, we take it (only exception is if the main image is svg).
+             The replacement graphic is a png which browsers are more likely able to render than the
+             original graphic which might have arbitrary formats. -->
+        <xsl:if test="(@loext:mime-type = 'image/svg+xml') or
+                            (not(following-sibling::draw:image) and
+                             not(preceding-sibling::draw:image[1]/@loext:mime-type = 'image/svg+xml'))">
             <xsl:choose>
                 <xsl:when test="ancestor::text:p or parent::text:span or parent::text:h or parent::draw:a or parent::text:a or text:ruby-base">
                     <!-- XHTML does not allow the mapped elements to contain paragraphs -->