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)
diff --git a/src/map.c b/src/map.c
index d99a84f..f3ff007 100644
--- a/src/map.c
+++ b/src/map.c
@@ -725,6 +725,9 @@
 				    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 @@
 	{
 	    // 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.
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index 7fdbdf6..e0008d6 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -1627,4 +1627,15 @@
   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
diff --git a/src/version.c b/src/version.c
index 74b4625..1d54137 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4819,
+/**/
     4818,
 /**/
     4817,