vim-patch:8.1.1365: source command doesn't check for the sandbox

Problem:    Source command doesn't check for the sandbox. (Armin Razmjou)
Solution:   Check for the sandbox when sourcing a file.
5357552140

src/nvim/getchar.c

@@ -1253,6 +1253,13 @@ openscript (
     EMSG(_(e_nesting));
     return;
   }
+
+  // Disallow sourcing a file in the sandbox, the commands would be executed
+  // later, possibly outside of the sandbox.
+  if (check_secure()) {
+    return;
+  }
+
   if (ignore_script)
     /* Not reading from script, also don't open one.  Warning message? */
     return;

src/nvim/testdir/test_source.vim

@@ -0,0 +1,10 @@
+" Tests for the :source command.
+
+func Test_source_sandbox()
+  new
+  call writefile(["Ohello\<Esc>"], 'Xsourcehello')
+  source! Xsourcehello | echo
+  call assert_equal('hello', getline(1))
+  call assert_fails('sandbox source! Xsourcehello', 'E48:')
+  bwipe!
+endfunc