bpo-45738: Fix computation of error location for invalid continuation (GH-29550)


characters in the parser
(cherry picked from commit 25835c518aa7446f3680b62c1fb43827e0f190d9)

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index 45b2785..3b79b7a 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -1487,7 +1487,13 @@ def func2():
     def test_invalid_line_continuation_error_position(self):
         self._check_error(r"a = 3 \ 4",
                           "unexpected character after line continuation character",
-                          lineno=1, offset=9)
+                          lineno=1, offset=8)
+        self._check_error('1,\\#\n2',
+                          "unexpected character after line continuation character",
+                          lineno=1, offset=4)
+        self._check_error('\nfgdfgf\n1,\\#\n2\n',
+                          "unexpected character after line continuation character",
+                          lineno=3, offset=4)
 
     def test_invalid_line_continuation_left_recursive(self):
         # Check bpo-42218: SyntaxErrors following left-recursive rules