patch 8.2.4819: unmapping simplified keys also deletes other mapping

Problem:    Unmapping simplified keys also deletes other mapping.
Solution:   Only unmap a mapping with m_simplified set. (closes #10270)

src/map.c

@@ -725,6 +725,9 @@ do_map(
 				    mpp = &(mp->m_next);
 				    continue;
 				}
+				if (did_simplify && keyround == 1
+							  && !mp->m_simplified)
+				    break;
 				// We reset the indicated mode bits. If nothing
 				// is left the entry is deleted below.
 				mp->m_mode &= ~mode;
@@ -814,7 +817,10 @@ do_map(
 	{
 	    // delete entry
 	    if (!did_it)
-		retval = 2;	// no match
+	    {
+		if (!did_simplify || keyround == 2)
+		    retval = 2;		// no match
+	    }
 	    else if (*keys == Ctrl_C)
 	    {
 		// If CTRL-C has been unmapped, reuse it for Interrupting.

src/testdir/test_mapping.vim

@@ -1627,4 +1627,15 @@ func Test_mouse_drag_insert_map()
   set mouse&
 endfunc
 
+func Test_unmap_simplfied()
+  map <C-I> foo
+  map <Tab> bar
+  call assert_equal('foo', maparg('<C-I>'))
+  call assert_equal('bar', maparg('<Tab>'))
+  unmap <C-I>
+  call assert_equal('', maparg('<C-I>'))
+  call assert_equal('bar', maparg('<Tab>'))
+  unmap <Tab>
+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 */
+/**/
+    4819,
 /**/
     4818,
 /**/