Dpkg::Source::Quilt: Clarify error message when patches fail to apply

There are other reasons besides patches with no fuzz, mention that the
patch could be malformed too, to make the error message less confusing.

debian/changelog

@@ -56,6 +56,9 @@ dpkg (1.17.11) UNRELEASED; urgency=low
     - Fix a typo in the BUGS section.
   * Mark the “and” between the filenames as regular format in dpkg-source(1).
   * Add --format and --ignore-bad-version to dpkg-source --help output.
+  * Clarify error message in Dpkg::Source::Quilt when patches fail to apply,
+    to note that the patch might be malformed (besides not accepting patches
+    with fuzz).
 
   [ Updated programs translations ]
   * Danish (Joe Dalton). Closes: #754127

scripts/Dpkg/Source/Quilt.pm

@@ -183,7 +183,7 @@ sub push {
                                  '-B', ".pc/$patch/", '--reject-file=-' ]);
     };
     if ($@) {
-        info(_g('fuzz is not allowed when applying patches'));
+        info(_g('the patch has fuzz which is not allowed, or is malformed'));
         info(_g("if patch '%s' is correctly applied by quilt, use '%s' to update it"),
              $patch, 'quilt refresh');
         $self->restore_quilt_backup_files($patch, %opts);