vim-patch:8.1.2293: join adds trailing space when second line is empty

Problem:    Join adds trailing space when second line is empty. (Brennan
            Vincent)
Solution:   Do not add a trailing space.
cc184cfb09

src/nvim/ops.c

@@ -3773,7 +3773,10 @@ int do_join(size_t count,
 
     if (insert_space && t > 0) {
       curr = skipwhite(curr);
-      if (*curr != ')' && currsize != 0 && endcurr1 != TAB
+      if (*curr != NUL
+          && *curr != ')'
+          && currsize != 0
+          && endcurr1 != TAB
           && (!has_format_option(FO_MBYTE_JOIN)
               || (utf_ptr2char(curr) < 0x100 && endcurr1 < 0x100))
           && (!has_format_option(FO_MBYTE_JOIN2)

src/nvim/testdir/test_join.vim

@@ -9,6 +9,27 @@ func Test_join_with_count()
   call setline(1, ['one', 'two', 'three', 'four'])
   normal 10J
   call assert_equal('one two three four', getline(1))
+
+  call setline(1, ['one', '', 'two'])
+  normal J
+  call assert_equal('one', getline(1))
+
+  call setline(1, ['one', ' ', 'two'])
+  normal J
+  call assert_equal('one', getline(1))
+
+  call setline(1, ['one', '', '', 'two'])
+  normal JJ
+  call assert_equal('one', getline(1))
+
+  call setline(1, ['one', ' ', ' ', 'two'])
+  normal JJ
+  call assert_equal('one', getline(1))
+
+  call setline(1, ['one', '', '', 'two'])
+  normal 2J
+  call assert_equal('one', getline(1))
+
   quit!
 endfunc