Avoid overflows when incrementing parameters in C

Any C function can receive maxinteger as an integer argument, and
therefore cannot increment it without some care (e.g., doing unsigned
arithmetic as the core does).

testes/nextvar.lua

@@ -43,6 +43,14 @@ assert(i == 4)
 assert(type(ipairs{}) == 'function' and ipairs{} == ipairs{})
 
 
+do   -- overflow (must wrap-around)
+  local f = ipairs{}
+  local k, v = f({[math.mininteger] = 10}, math.maxinteger)
+  assert(k == math.mininteger and v == 10)
+  k, v = f({[math.mininteger] = 10}, k)
+  assert(k == nil)
+end
+
 if not T then
   (Message or print)
     ('\n >>> testC not active: skipping tests for table sizes <<<\n')
@@ -499,6 +507,15 @@ do   -- testing table library with metamethods
 end
 
 
+do   -- testing overflow in table.insert (must wrap-around)
+
+  local t = setmetatable({},
+            {__len = function () return math.maxinteger end})
+  table.insert(t, 20)
+  local k, v = next(t)
+  assert(k == math.mininteger and v == 20)
+end
+
 if not T then
   (Message or print)
     ('\n >>> testC not active: skipping tests for table library on non-tables <<<\n')

testes/utf8.lua

@@ -112,6 +112,12 @@ do
   end
   errorcodes("ab\xff")
   errorcodes("\u{110000}")
+
+  -- calling interation function with invalid arguments
+  local f = utf8.codes("")
+  assert(f("", 2) == nil)
+  assert(f("", -1) == nil)
+  assert(f("", math.mininteger) == nil)
 end
 
 -- error in initial position for offset