No need to recheck close method before calling it

A to-be-closed variable is constant and it must have a close metamethod
when it is created. A program has to go out of its way (e.g., by
changing the variable's metamethod) to invalidate that check. So,
it is not worth to test that again. If the program tampers with the
metamethod, Lua will raise a regular error when attempting to call it.

testes/locals.lua

@@ -459,8 +459,50 @@ do   -- errors due to non-closable values
     getmetatable(xyz).__close = nil   -- remove metamethod
   end
   local stat, msg = pcall(foo)
-  assert(not stat and
-    string.find(msg, "attempt to close non%-closable variable 'xyz'"))
+  assert(not stat and string.find(msg, "attempt to call a nil value"))
+end
+
+
+do   -- tbc inside close methods
+  local track = {}
+  local function foo ()
+    local x <close> = func2close(function ()
+      local xx <close> = func2close(function (_, msg)
+        assert(msg == nil)
+        track[#track + 1] = "xx"
+      end)
+      track[#track + 1] = "x"
+    end)
+    track[#track + 1] = "foo"
+    return 20, 30, 40
+  end
+  local a, b, c, d = foo()
+  assert(a == 20 and b == 30 and c == 40 and d == nil)
+  assert(track[1] == "foo" and track[2] == "x" and track[3] == "xx")
+
+  -- again, with errors
+  local track = {}
+  local function foo ()
+    local x0 <close> = func2close(function (_, msg)
+      assert(msg == 202)
+        track[#track + 1] = "x0"
+    end)
+    local x <close> = func2close(function ()
+      local xx <close> = func2close(function (_, msg)
+        assert(msg == 101)
+        track[#track + 1] = "xx"
+        error(202)
+      end)
+      track[#track + 1] = "x"
+      error(101)
+    end)
+    track[#track + 1] = "foo"
+    return 20, 30, 40
+  end
+  local st, msg = pcall(foo)
+  assert(not st and msg == 202)
+  assert(track[1] == "foo" and track[2] == "x" and track[3] == "xx" and
+         track[4] == "x0")
 end