py/objstr: strip: Don't strip "\0" by default.

An issue was due to incorrectly taking size of default strip characters
set.

py/objstr.c

@@ -777,7 +777,7 @@ STATIC mp_obj_t str_uni_strip(int type, size_t n_args, const mp_obj_t *args) {
 
     if (n_args == 1) {
         chars_to_del = whitespace;
-        chars_to_del_len = sizeof(whitespace);
+        chars_to_del_len = sizeof(whitespace) - 1;
     } else {
         if (mp_obj_get_type(args[1]) != self_type) {
             bad_implicit_conversion(args[1]);

tests/basics/string_strip.py

@@ -32,6 +32,13 @@ print("a ".strip())
 print("a ".lstrip())
 print("a ".rstrip())
 
+# \0 used to give a problem
+
+print("\0abc\0".strip())
+print("\0abc\0".lstrip())
+print("\0abc\0".rstrip())
+print("\0abc\0".strip("\0"))
+
 # Test that stripping unstrippable string returns original object
 s = "abc"
 print(id(s.strip()) == id(s))