patch 8.2.2207: illegal memory access if popup menu items are changed

Problem:    Illegal memory access if popup menu items are changed while the
            menu is visible. (Tomáš Janoušek)
Solution:   Make a copy of the text. (closes #7537)
diff --git a/src/testdir/dumps/Test_popup_command_04.dump b/src/testdir/dumps/Test_popup_command_04.dump
new file mode 100644
index 0000000..c14576c
--- /dev/null
+++ b/src/testdir/dumps/Test_popup_command_04.dump
@@ -0,0 +1,20 @@
+|o+0&#ffffff0|n|e| |t|w|o| |t|h|r|e@1| |f|o|u|r| |f|i|v|e| @51
+|a|n|d| |o|n|e| |t|w|o| |X|t|h|r|e@1| |f|o|u|r| |f|i|v|e| @46
+|o|n|e| |m|o|r|e| |t|w| +0#0000001#ffd7ff255|U|n|d|o| @12| +0#0000000#ffffff0@45
+|~+0#4040ff13&| @9| +0#0000001#ffd7ff255@17| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|P|a|s|t|e| @11| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255@17| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|S|e|l|e|c|t| |W|o|r|d| @5| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|S|e|l|e|c|t| |S|e|n|t|e|n|c|e| @1| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|S|e|l|e|c|t| |P|a|r|a|g|r|a|p|h| | +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|S|e|l|e|c|t| |L|i|n|e| @5| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|S|e|l|e|c|t| |B|l|o|c|k| @4| +0#4040ff13#ffffff0@45
+|~| @9| +0#0000001#ffd7ff255|S|e|l|e|c|t| |A|l@1| @6| +0#4040ff13#ffffff0@45
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|c+0#0000000&|h|a|n|g|e|d> @67
diff --git a/src/testdir/dumps/Test_popup_command_05.dump b/src/testdir/dumps/Test_popup_command_05.dump
new file mode 100644
index 0000000..de1c95e
--- /dev/null
+++ b/src/testdir/dumps/Test_popup_command_05.dump
@@ -0,0 +1,20 @@
+|o+0&#ffffff0|n|e| |t|w|o| |t|h|r|e@1| |f|o|u|r| |f|i|v|e| @51
+|a|n|d| |o|n|e| |t|w|o| >X|t|h|r|e@1| |f|o|u|r| |f|i|v|e| @46
+|o|n|e| |m|o|r|e| |t|w|o| |t|h|r|e@1| |f|o|u|r| |f|i|v|e| @46
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|p+0#0000000&|a|s|t|e|d| @50|2|,|1|3| @9|A|l@1| 
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index 28481b3..9175ff1 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -859,18 +859,30 @@
   call assert_fails('popup Foo', 'E337:')
   unmenu Test.Foo
 
+  let script =<< trim END
+    func StartTimer()
+      call timer_start(100, {-> ChangeMenu()})
+    endfunc
+    func ChangeMenu()
+      nunmenu PopUp.&Paste
+      nnoremenu 1.40 PopUp.&Paste :echomsg "pasted"<CR>
+      echomsg 'changed'
+    endfunc
+  END
+  call writefile(script, 'XtimerScript')
+
   let lines =<< trim END
 	one two three four five
 	and one two Xthree four five
 	one more two three four five
   END
   call writefile(lines, 'Xtest')
-  let buf = RunVimInTerminal('Xtest', {})
+  let buf = RunVimInTerminal('-S XtimerScript Xtest', {})
   call term_sendkeys(buf, ":source $VIMRUNTIME/menu.vim\<CR>")
   call term_sendkeys(buf, "/X\<CR>:popup PopUp\<CR>")
   call VerifyScreenDump(buf, 'Test_popup_command_01', {})
 
-  " Select a word
+  " go to the Paste entry in the menu
   call term_sendkeys(buf, "jj")
   call VerifyScreenDump(buf, 'Test_popup_command_02', {})
 
@@ -879,8 +891,20 @@
   call VerifyScreenDump(buf, 'Test_popup_command_03', {})
 
   call term_sendkeys(buf, "\<Esc>")
+
+  " Set a timer to change a menu entry while it's displayed.  The text should
+  " not change but the command does.  Making the screendump also verifies that
+  " "changed" shows up, which means the timer triggered
+  call term_sendkeys(buf, "/X\<CR>:call StartTimer() | popup PopUp\<CR>")
+  call VerifyScreenDump(buf, 'Test_popup_command_04', {})
+
+  " Select the Paste entry, executes the changed menu item.
+  call term_sendkeys(buf, "jj\<CR>")
+  call VerifyScreenDump(buf, 'Test_popup_command_05', {})
+
   call StopVimInTerminal(buf)
   call delete('Xtest')
+  call delete('XtimerScript')
 endfunc
 
 func Test_popup_complete_backwards()