patch 8.2.1512: failure after trinary expression fails

Problem:    Failure after trinary expression fails.
Solution:   Restore eval_flags. (Yasuhiro Matsumoto, closes #6776)
diff --git a/src/testdir/test_vimscript.vim b/src/testdir/test_vimscript.vim
index 9dd5fc7..f17e908 100644
--- a/src/testdir/test_vimscript.vim
+++ b/src/testdir/test_vimscript.vim
@@ -7445,6 +7445,30 @@
   call StopVimInTerminal(buf)
 endfunc
 
+" Test for issue6776              {{{1
+func Test_trinary_expression()
+  try
+    call eval('0 ? 0')
+  catch
+  endtry
+  " previous failure should not cause next expression to fail
+  call assert_equal(v:false, eval(string(v:false)))
+
+  try
+    call eval('0 ? "burp')
+  catch
+  endtry
+  " previous failure should not cause next expression to fail
+  call assert_equal(v:false, eval(string(v:false)))
+
+  try
+    call eval('1 ? 0 : "burp')
+  catch
+  endtry
+  " previous failure should not cause next expression to fail
+  call assert_equal(v:false, eval(string(v:false)))
+endfunction
+
 "-------------------------------------------------------------------------------
 " Modelines								    {{{1
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker