ImageMagick output might sometimes be 0, even when there's an error

[adrianpike]

mogrify: unable to read font `Arial-Regular' @ warning/annotate.c/RenderType/871.
mogrify: delegate library support not built-in `/usr/share/fonts/default/Type1/n019003l.pfb' (Freetype) @ warning/annotate.c/RenderFreetype/1526.
mogrify: no decode delegate for this image format `/tmp/magick-O-5PYksV-00000001' @ error/constitute.c/ReadImage/544.
mogrify: Postscript delegate failed `/tmp/magick-tJaibFh7': No such file or directory @ error/ps.c/ReadPSImage/830.
mogrify: unable to read font `Arial-Regular' @ warning/annotate.c/RenderType/871.
mogrify: delegate library support not built-in `/usr/share/fonts/default/Type1/n019003l.pfb' (Freetype) @ warning/annotate.c/RenderFreetype/1526.
mogrify: no decode delegate for this image format `/tmp/magick-SULRxCJ5-00000001' @ error/constitute.c/ReadImage/544.
mogrify: Postscript delegate failed `/tmp/magick-t3G0dzwd': No such file or directory @ error/ps.c/ReadPSImage/830.
[ec2-user@ip-10-108-17-189 tmp]$ echo $?
0
[ec2-user@ip-10-108-17-189 tmp]$

Looks like ImageMagick returns 0 sometimes even when it wasn't able to make an image, so even though there's a check for this no-font scenario, it never reaches it (https://github.com/carnesmedia/thumbkit/blob/master/lib/thumbkit/processor/text.rb#L88)