patch 8.2.4148: deleting any mapping may cause <ScritpCmd> to fail

Problem:    Deleting any mapping may cause <ScritpCmd> to not set the script
            context.
Solution:   Only reset last_used_map if it is the deleted mapping.
            (closes #9568)
diff --git a/src/getchar.c b/src/getchar.c
index ff71952..c0dfc2b 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -3836,8 +3836,9 @@
 
 #if defined(FEAT_EVAL) || defined(PROTO)
     void
-reset_last_used_map(void)
+reset_last_used_map(mapblock_T *mp)
 {
-    last_used_map = NULL;
+    if (last_used_map == mp)
+	last_used_map = NULL;
 }
 #endif
diff --git a/src/map.c b/src/map.c
index f16397a..ff117dc 100644
--- a/src/map.c
+++ b/src/map.c
@@ -86,7 +86,7 @@
     *mpp = mp->m_next;
     vim_free(mp);
 #ifdef FEAT_EVAL
-    reset_last_used_map();
+    reset_last_used_map(mp);
 #endif
 }
 
diff --git a/src/proto/getchar.pro b/src/proto/getchar.pro
index 2d791e5..a034257 100644
--- a/src/proto/getchar.pro
+++ b/src/proto/getchar.pro
@@ -53,5 +53,5 @@
 int fix_input_buffer(char_u *buf, int len);
 int input_available(void);
 int do_cmdkey_command(int key, int flags);
-void reset_last_used_map(void);
+void reset_last_used_map(mapblock_T *mp);
 /* vim: set ft=c : */
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index a556362..69de22b 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -1439,6 +1439,22 @@
   unlet g:func_called
 endfunc
 
+func Test_map_script_cmd_survives_unmap()
+  let lines =<< trim END
+      vim9script
+      var n = 123
+      nnoremap <F4> <ScriptCmd><CR>
+      autocmd CmdlineEnter * silent! nunmap <F4>
+      nnoremap <F3> :<ScriptCmd>eval setbufvar(bufnr(), "result", n)<CR>
+      feedkeys("\<F3>\<CR>", 'xct')
+      assert_equal(123, b:result)
+  END
+  call CheckScriptSuccess(lines)
+
+  nunmap <F3>
+  unlet b:result
+endfunc
+
 " Test for using <script> with a map to remap characters in rhs
 func Test_script_local_remap()
   new
diff --git a/src/version.c b/src/version.c
index 1ca0a22..d9307ec 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4148,
+/**/
     4147,
 /**/
     4146,