Workaround progressbar failure if minion is behind syndic.

salt/output/progress.py

@@ -23,7 +23,14 @@ def output(ret, bar, **kwargs):  # pylint: disable=unused-argument
     Update the progress bar
     '''
     if 'return_count' in ret:
-        bar.update(ret['return_count'])
+        val = ret['return_count']
+        # Avoid to fail if targets are behind a syndic. In this case actual return count will be
+        # higher than targeted by MoM itself.
+        # TODO: implement a way to get the proper target minions count and remove this workaround.
+        # Details are in #44239.
+        if val > bar.maxval:
+            bar.maxval = val
+        bar.update(val)
     return ''