Issue #11272: Fix input() and sys.stdin for Windows newline

On Windows, input() strips '\r' (and not only '\n'), and sys.stdin uses
universal newline (replace '\r\n' by '\n').
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 42bc809..c6bb16c 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1618,6 +1618,7 @@
         PyObject *stdin_encoding;
         char *stdin_encoding_str;
         PyObject *result;
+        size_t len;
 
         stdin_encoding = PyObject_GetAttrString(fin, "encoding");
         if (!stdin_encoding)
@@ -1682,19 +1683,23 @@
             Py_DECREF(stdin_encoding);
             return NULL;
         }
-        if (*s == '\0') {
+
+        len = strlen(s);
+        if (len == 0) {
             PyErr_SetNone(PyExc_EOFError);
             result = NULL;
         }
-        else { /* strip trailing '\n' */
-            size_t len = strlen(s);
+        else {
             if (len > PY_SSIZE_T_MAX) {
                 PyErr_SetString(PyExc_OverflowError,
                                 "input: input too long");
                 result = NULL;
             }
             else {
-                result = PyUnicode_Decode(s, len-1, stdin_encoding_str, NULL);
+                len--;   /* strip trailing '\n' */
+                if (len != 0 && s[len-1] == '\r')
+                    len--;   /* strip trailing '\r' */
+                result = PyUnicode_Decode(s, len, stdin_encoding_str, NULL);
             }
         }
         Py_DECREF(stdin_encoding);