Based on the issue description, I have enough information to create the patch. The issue states:

1. The error occurs at line 673: `for ps_name, xs_names in stream:`
2. The bug is in `backend_ps.py` 
3. Adding `if curr_stream:` before line 669 fixes the bug
4. The issue is that when there's an empty line in the text, `curr_stream` is None, and when it gets appended to `stream`, iterating over `stream` tries to unpack None

Looking at the typical pattern in matplotlib's PostScript backend for text rendering, the issue is that:
1. Text is processed line by line
2. For empty lines, no font/character stream is generated (returns None)
3. The code appends this None to a list
4. Later, when iterating over the list, it tries to unpack None

The fix is to check if `curr_stream` is not None before appending it to the stream list or before iterating.

Based on the user's suggestion and the error traceback, the fix should be adding a check `if curr_stream:` before line 669. Looking at typical matplotlib code structure, this is likely before the append operation.

Let me construct the patch based on the information provided:

--- a/lib/matplotlib/backends/backend_ps.py
+++ b/lib/matplotlib/backends/backend_ps.py
@@ -666,6 +666,8 @@
                     else:
                         curr_stream.append((xp, name))
                 prev_chunk = chunk
+            if curr_stream:
                 stream.append(curr_stream)
         self.set_color(*gc.get_rgb())
         for ps_name, xs_names in stream: