fix #1173 generate a thumbnail of a first page

src/main/assemblies/files/generate-thumbnail

@@ -9,11 +9,11 @@ if [ x"$CMD_TYPE" = "xmsoffice" ] ; then
   TARGET_FILE=`echo $URL | sed -e "s#^file:/*#/#g"`
   TMP_FILE=/tmp/thumbnail.$$.pdf
   unoconv -e PageRange=1-1 -o $TMP_FILE -f pdf $TARGET_FILE
-  convert -thumbnail $IMAGE_SIZE $TMP_FILE $OUTPUT_FILE
+  convert -thumbnail $IMAGE_SIZE ${TMP_FILE}[0] $OUTPUT_FILE
   rm $TMP_FILE
 elif [ x"$CMD_TYPE" = "xpdf" ] ; then
   TARGET_FILE=`echo $URL | sed -e "s#^file:/*#/#g"`
-  convert -thumbnail $IMAGE_SIZE $TARGET_FILE $OUTPUT_FILE
+  convert -thumbnail $IMAGE_SIZE ${TARGET_FILE}[0] $OUTPUT_FILE
 else
   echo "Unsupported type: $CMD_TYPE"
   exit 1