bpo-17735: inspect.findsource now raises OSError when co_lineno is out of range (GH-23633)

This can happen when a file was edited after it was imported.
(cherry picked from commit 2e0760bb2e)

Co-authored-by: Irit Katriel <iritkatriel@yahoo.com>

Lib/inspect.py

@@ -864,7 +864,12 @@ def findsource(object):
         lnum = object.co_firstlineno - 1
         pat = re.compile(r'^(\s*def\s)|(\s*async\s+def\s)|(.*(?<!\w)lambda(:|\s))|^(\s*@)')
         while lnum > 0:
-            if pat.match(lines[lnum]): break
+            try:
+                line = lines[lnum]
+            except IndexError:
+                raise OSError('lineno is out of bounds')
+            if pat.match(line):
+                break
             lnum = lnum - 1
         return lines, lnum
     raise OSError('could not find code object')