patch 8.1.1160: termcodes test would fail in a very big terminal

Problem:    Termcodes test would fail in a very big terminal.
Solution:   Bail out when the row is larger than what will work. (Dominique
            Pelle, closes #4246)
diff --git a/src/testdir/test_termcodes.vim b/src/testdir/test_termcodes.vim
index 633e021..949fa94 100644
--- a/src/testdir/test_termcodes.vim
+++ b/src/testdir/test_termcodes.vim
@@ -118,6 +118,12 @@
     let rowseparator = winheight(0) + 1
     let row = rowseparator
     let col = 1
+
+    if ttymouse_val ==# 'xterm' && row > 223
+      " When 'ttymouse' is 'xterm', row/col bigger than 223 are not supported.
+      continue
+    endif
+
     call MouseLeftClick(row, col)
 
     let row -= 1
@@ -168,6 +174,12 @@
     let rowstatusline = winheight(0) + 1
     let row = rowstatusline
     let col = 1
+
+    if ttymouse_val ==# 'xterm' && row > 223
+      " When 'ttymouse' is 'xterm', row/col bigger than 223 are not supported.
+      continue
+    endif
+
     call MouseLeftClick(row, col)
     let row -= 1
     call MouseLeftDrag(row, col)