patch 8.0.1559: build failure without GUI

Problem:    Build failure without GUI.
Solution:   Adjust #ifdef for get_fpos_of_mouse().
diff --git a/src/version.c b/src/version.c
index f697216..716b29b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -779,6 +779,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1559,
+/**/
     1558,
 /**/
     1557,