dpkg-genchanges: Clarify changes description open error

debian/changelog

@@ -89,6 +89,7 @@ dpkg (1.18.0) UNRELEASED; urgency=low
     - Use “<enter>” instead of “return” or “enter” in input prompts.
     - Say directory instead of dir in output messages.
     - Merge the same dpkg-scanpackages warning messages into a single line.
+    - Clarify dpkg-genchanges changes description open error.
 
   [ Raphaël Hertzog ]
   * Drop myself from Uploaders.

scripts/dpkg-genchanges.pl

@@ -419,7 +419,7 @@ foreach (keys %{$changelog}) {
 
 if ($changesdescription) {
     open(my $changes_fh, '<', $changesdescription)
-        or syserr(g_('read changesdescription'));
+        or syserr(g_('cannot read %s'), $changesdescription);
     $fields->{'Changes'} = "\n" . file_slurp($changes_fh);
     close($changes_fh);
 }