fix: guard debug stack walk

Author: windsornguyen

uvloop/cbhandles.pyx

@@ -424,7 +424,16 @@ cdef extract_stack():
         return
 
     try:
-        stack = tb_StackSummary.extract(tb_walk_stack(f),
+        frames = []
+        while f is not None:
+            lineno = getattr(f, "f_lineno", None)
+            if lineno is None:
+                break
+            if getattr(f, "f_code", None) is None:
+                break
+            frames.append((f, lineno))
+            f = getattr(f, "f_back", None)
+        stack = tb_StackSummary.extract(frames,
                                         limit=DEBUG_STACK_DEPTH,
                                         lookup_lines=False)
     finally: