Fix regression under Windows following b75b41237380 (from issue #13392)
diff --git a/Python/import.c b/Python/import.c
index 3c3e504..64197d7 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -1267,6 +1267,11 @@
         PyErr_Clear();
         return;
     }
+    if (PyUnicode_CopyCharacters(cpathname_tmp, 0,
+                                 cpathname, 0, cpathname_len) < 0) {
+        PyErr_Clear();
+        return;
+    }
     PyUnicode_WriteChar(cpathname_tmp, cpathname_len + 0, '.');
     PyUnicode_WriteChar(cpathname_tmp, cpathname_len + 1, 't');
     PyUnicode_WriteChar(cpathname_tmp, cpathname_len + 2, 'm');