Fix compare output in HTML test driver

Newer versions output two numbers instead of just one, so we pick the
first number:

  ++ compare -metric AE b-div.html_wdir/{html.png,ref.png,diff.png}
  + diffcount='0 (0)'
  + '[' '0 (0)' = 0 ']'
  + echo FAIL
  FAIL

Author: rodarima

test/html/driver.sh

@@ -93,7 +93,7 @@ function test_file() {
   render_page "$ref_file" "$wdir/ref.png"
 
   # AE = Absolute Error count of the number of different pixels
-  diffcount=$(compare -metric AE "$wdir/html.png" "$wdir/ref.png" "$wdir/diff.png" 2>&1 || true)
+  diffcount=$(compare -metric AE "$wdir/html.png" "$wdir/ref.png" "$wdir/diff.png" 2>&1 | cut -d ' ' -f 1 || true)
 
   # The test passes only if both images are identical
   if [ "$diffcount" = "0" ]; then