Fix UnicodeDecodeError exception catching.

`str_lines` is a generator object, it won't be executed until Tokenizer() uses it.

PiperOrigin-RevId: 499824005

python/google/protobuf/internal/text_format_test.py

@@ -786,6 +786,12 @@ class TextFormatParserTests(TextFormatBase):
     self.assertEqual(message_module.TestAllTypes(), message)
 
   def testParseInvalidUtf8(self, message_module):
+    message = message_module.TestAllTypes()
+    text = b'invalid<\xc3\xc3>'
+    with self.assertRaises(text_format.ParseError):
+      text_format.Parse(text, message)
+
+  def testParseInvalidUtf8Value(self, message_module):
     message = message_module.TestAllTypes()
     text = 'repeated_string: "\\xc3\\xc3"'
     with self.assertRaises(text_format.ParseError) as e:

python/google/protobuf/text_format.py

@@ -859,9 +859,9 @@ class _Parser(object):
       str_lines = (
           line if isinstance(line, str) else line.decode('utf-8')
           for line in lines)
+      tokenizer = Tokenizer(str_lines)
     except UnicodeDecodeError as e:
-      raise self._StringParseError(e)
+      raise ParseError from e
-    tokenizer = Tokenizer(str_lines)
     if message:
       self.root_type = message.DESCRIPTOR.full_name
     while not tokenizer.AtEnd():