Create changes file if none exists

This was noticed in a CI generated package with only a _service file,
which now fails because I made rpm error when it finds no changes file
in Factory.

Fixes: https://bugzilla.suse.com/show_bug.cgi?id=1220540

TarSCM/tasks.py

@@ -292,6 +292,13 @@ def _process_changes(self, args, ver, changesversion, detected_changes):
             changesversion = self.get_version()
 
         logging.debug("Searching for '*.changes' in %s", os.getcwd())
+        changesfiles = glob.glob('*.changes')
+        if not changesfiles:
+            if args.filename:
+                basename = args.filename
+            else:
+                basename = os.path.basename(self.scm_object.clone_dir)
+            changesfiles = [basename + ".changes"]
         for filename in glob.glob('*.changes'):
             new_changes_file = os.path.join(args.outdir, filename)
             shutil.copy(filename, new_changes_file)