vim-patch:7.4.1051

Problem:    Segfault when unletting "count".
Solution:   Check for readonly and locked first. (Dominique Pelle)
            Add a test.

af8af8bfac

src/nvim/testdir/test_unlet.vim

@@ -0,0 +1,26 @@
+" Tests for :unlet
+
+func Test_read_only()
+  try
+    " this caused a crash
+    unlet count
+  catch
+    call assert_true(v:exception =~ ':E795:')
+  endtry
+endfunc
+
+func Test_existing()
+  let does_exist = 1
+  call assert_true(exists('does_exist'))
+  unlet does_exist
+  call assert_false(exists('does_exist'))
+endfunc
+
+func Test_not_existing()
+  unlet! does_not_exist
+  try
+    unlet does_not_exist
+  catch
+    call assert_true(v:exception =~ ':E108:')
+  endtry
+endfunc