patch 8.0.0537: illegal memory access with :z and large count

Problem:    Illegal memory access with :z and large count.
Solution:   Check for number overflow, using long instead of int. (Dominique
            Pelle, closes #1612)

src/testdir/test_ex_z.vim

@@ -0,0 +1,78 @@
+" Test :z
+
+func Test_z()
+  call setline(1, range(1, 100))
+
+  let a = execute('20z3')
+  call assert_equal("\n20\n21\n22", a)
+  call assert_equal(22, line('.'))
+  " 'window' should be set to the {count} value.
+  call assert_equal(3, &window)
+
+  " If there is only one window, then twice the amount of 'scroll' is used.
+  set scroll=2
+  let a = execute('20z')
+  call assert_equal("\n20\n21\n22\n23", a)
+  call assert_equal(23, line('.'))
+
+  let a = execute('20z+3')
+  " FIXME: I would expect the same result as '20z3' but it
+  " gives "\n21\n22\n23" instead. Bug in Vim or in ":help :z"?
+  "call assert_equal("\n20\n21\n22", a)
+  "call assert_equal(22, line('.'))
+
+  let a = execute('20z-3')
+  call assert_equal("\n18\n19\n20", a)
+  call assert_equal(20, line('.'))
+
+  let a = execute('20z=3')
+  call assert_match("^\n18\n19\n-\\+\n20\n-\\+\n21\n22$", a)
+  call assert_equal(20, line('.'))
+
+  let a = execute('20z^3')
+  call assert_equal("\n14\n15\n16\n17", a)
+  call assert_equal(17, line('.'))
+
+  let a = execute('20z.3')
+  call assert_equal("\n19\n20\n21", a)
+  call assert_equal(21, line('.'))
+
+  let a = execute('20z#3')
+  call assert_equal("\n 20 20\n 21 21\n 22 22", a)
+  call assert_equal(22, line('.'))
+
+  let a = execute('20z#-3')
+  call assert_equal("\n 18 18\n 19 19\n 20 20", a)
+  call assert_equal(20, line('.'))
+
+  let a = execute('20z#=3')
+  call assert_match("^\n 18 18\n 19 19\n-\\+\n 20 20\n-\\+\n 21 21\n 22 22$", a)
+  call assert_equal(20, line('.'))
+
+  " Test with {count} bigger than the number of lines in buffer.
+  let a = execute('20z1000')
+  call assert_match("^\n20\n21\n.*\n99\n100$", a)
+  call assert_equal(100, line('.'))
+
+  let a = execute('20z-1000')
+  call assert_match("^\n1\n2\n.*\n19\n20$", a)
+  call assert_equal(20, line('.'))
+
+  let a = execute('20z=1000')
+  call assert_match("^\n1\n.*\n-\\+\n20\n-\\\+\n.*\n100$", a)
+  call assert_equal(20, line('.'))
+
+  call assert_fails('20z=a', 'E144:')
+
+  set window& scroll&
+  bw!
+endfunc
+
+func Test_z_bug()
+  " This used to access invalid memory as a result of an integer overflow
+  " and freeze vim.
+  normal ox
+  normal Heat
+  z777777776666666
+  ')
+endfunc