Security update for GraphicsMagick (low)

This update for GraphicsMagick fixes the following security issue:

• CVE-2018-16323: ReadXBMImage left data uninitialized when processing an
  XBM file that has a negative pixel value. If the affected code was used
  as a library loaded into a process that includes sensitive information,
  that information sometimes can be leaked via the image data
  (bsc#1106855).