patch 8.0.0556: getting window position fails if GUI and term possible

Problem:    Getting the window position fails if both the GUI and term
            code is built in.
Solution:   Return after getting the GUI window position. (Kazunobu Kuriyama)
diff --git a/src/version.c b/src/version.c
index 7cf7644..efb2ef3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    556,
+/**/
     555,
 /**/
     554,