Issue #7858: Raise an error properly when os.utime() fails under Windows
on an existing file.

(this does not seem to be easily testable)
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 0cd6340..a37efca 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -3256,6 +3256,7 @@
            something is wrong with the file, when it also
            could be the time stamp that gives a problem. */
         win32_error("utime", NULL);
+        goto done;
     }
     Py_INCREF(Py_None);
     result = Py_None;