Description:
------------
Using the function imagettftext of the GD library fails with some ttf fonts; instead of the letters appears only little boxes, similar to the ones showed in the windows charachter map application when a gliph is not present in a font.

The behavior was OK on the 4.3.9 version

The code works if, for example, i use another ttf file (arial.ttf)

Reproduce code:
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<?php
  header("Content-type: image/gif");
  $im = imagecreate(600, 200);
  $white = imagecolorallocate($im, 221, 221, 221);
  $black = imagecolorallocate($im, 51, 0, 153);
  imagettftext($im, 30, 0, 100, 100, $black, "font/rbb.ttf" ,"This is a test");
  imagegif($im);
  imagedestroy($im);
?>

The font rbb.ttf can be downloaded at

http://www.revelshblindbeholders.net/font/rbb.ttf

Expected result:
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The result should be a gray box with the text "This is a test" written with the chosen font

Actual result:
--------------
The gray box appear, but instead of the text i see only little boxes, alike the ones showed in the Win char map when a char is not implemented within the font.

The code works if, for example i use another ttf file (arial.ttf)