eZImageManager goes into an infinite loop when processing an image alias that contains filters from more than one image handler.

Steps to reproduce

• Make sure that both GD and ImageMagick are configured correctly
• Add the following to image.ini:

  [AliasSettings]
  AliasList[]=multihandler
  
  [multihandler]
  Reference=
  Filters[]
  # From GD
  Filters[]=luminance/gray
  # From ImageMagick
  Filters[]=filter/swirl=210
  

• Load an image using the multihandler alias