patch 8.0.1320: popup test fails on GUI-only build

Problem:    Popup test fails on GUI-only build.
Solution:   Don't test balloon_split() when it's not available.
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index bfccb74..2bb9b32 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -704,6 +704,9 @@
 endfunc
 
 func Test_balloon_split()
+  if !exists('*balloon_split')
+    return
+  endif
   call assert_equal([
         \ 'one two three four one two three four one two thre',
         \ 'e four',
diff --git a/src/version.c b/src/version.c
index 2e52e80..324a360 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1320,
+/**/
     1319,
 /**/
     1318,