patch 8.2.2870: CmdlineChange event triggered twice for CTRL-R

Problem:    CmdlineChange event triggered twice for CTRL-R.
Solution:   Return CMDLINE_NOT_CHANGED from cmdline_insert_reg().
            (closes #8219)

src/ex_getln.c

@@ -1253,8 +1253,11 @@ cmdline_insert_reg(int *gotesc UNUSED)
 	}
 #endif
     }
+    // remove the double quote
     redrawcmd();
-    return CMDLINE_CHANGED;
+
+    // The text has been stuffed, the command line didn't change yet.
+    return CMDLINE_NOT_CHANGED;
 }
 
 /*

src/testdir/test_cmdline.vim

@@ -1810,6 +1810,12 @@ func Test_cmd_map_cmdlineChanged()
   call feedkeys(":\<F1>\<CR>", 'xt')
   call assert_equal(['l', 'ls'], g:log)
 
+  let @b = 'b'
+  cnoremap <F1> a<C-R>b
+  let g:log = []
+  call feedkeys(":\<F1>\<CR>", 'xt')
+  call assert_equal(['a', 'ab'], g:log)
+
   unlet g:log
   cunmap <F1>
   augroup test

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2870,
 /**/
     2869,
 /**/