patch 8.2.0904: assuming modifyOtherKeys for rhs of mapping

Problem:    Assuming modifyOtherKeys for rhs of mapping.
Solution:   Ignore seenModifyOtherKeys for mapped characters. (closes #6200)

src/getchar.c

@@ -2355,7 +2355,8 @@ handle_mapping(
 	    // Skip ":lmap" mappings if keys were mapped.
 	    if (mp->m_keys[0] == tb_c1
 		    && (mp->m_mode & local_State)
-		    && !(mp->m_simplified && seenModifyOtherKeys)
+		    && !(mp->m_simplified && seenModifyOtherKeys
+						     && typebuf.tb_maplen == 0)
 		    && ((mp->m_mode & LANGMAP) == 0 || typebuf.tb_maplen == 0))
 	    {
 #ifdef FEAT_LANGMAP

src/testdir/test_gui.vim

@@ -856,4 +856,14 @@ func Test_gui_run_cmd_in_terminal()
   let &guioptions = save_guioptions
 endfunc
 
+func Test_gui_recursive_mapping()
+  nmap ' <C-W>
+  nmap <C-W>a :let didit = 1<CR>
+  call feedkeys("'a", 'xt')
+  call assert_equal(1, didit)
+
+  nunmap '
+  nunmap <C-W>a
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    904,
 /**/
     903,
 /**/