Bug#792413: patchutils: filterdiff doesn't check for errors when processing -X / -I option

[patchutils.bug@discard.email]

Package: patchutils
Version: 0.3.3-1
 
filterdiff doesn't check for fopen() errors when processing the
-X (exclude-from-file) and -I (--include-from-file) options.
 
This means that
filterdiff -X exclude.file my.patch
behaves like cat if exclude.file doesn't exist (e.g. if you mistype
the filename).
 
I think it would be more sensible if filterdiff exited with an error
in this case.