patch 8.1.0571: non-silent execute() resets display column to zero

Problem:    Non-silent execute() resets display column to zero.
Solution:   Keep the display column as-is.
diff --git a/src/testdir/test_execute_func.vim b/src/testdir/test_execute_func.vim
index 7b3cf21..b84fbeb 100644
--- a/src/testdir/test_execute_func.vim
+++ b/src/testdir/test_execute_func.vim
@@ -61,3 +61,20 @@
   endfor
   call assert_equal('abcdxyz', text)
 endfunc
+
+func Test_execute_not_silent()
+  echo ''
+  echon 'abcd'
+  let x = execute('echon 234', '')
+  echo 'xyz'
+  let text1 = ''
+  for col in range(1, 8)
+    let text1 .= nr2char(screenchar(&lines - 1, col))
+  endfor
+  call assert_equal('abcd234 ', text1)
+  let text2 = ''
+  for col in range(1, 4)
+    let text2 .= nr2char(screenchar(&lines, col))
+  endfor
+  call assert_equal('xyz ', text2)
+endfunc