Fix a small compile issue with latest Crystal version + Bug with non-ascii strings and comments

spec/lua/stack/chunk_spec.cr

@@ -43,6 +43,23 @@ module Lua::StackMixin
         )).should be_a Function
         s.close
       end
+
+      context "with multibyte UTF-8 characters" do
+        it "keeps the full chunk when a comment contains multibyte characters" do
+          s = Stack.new
+          s.run(%q(
+            -- é à ç — สวัสดี 你好
+            return 42
+          )).should eq 42
+          s.close
+        end
+
+        it "passes multibyte bytes through inside string literals" do
+          s = Stack.new
+          s.run(%q( return "é — สวัสดี 你好" )).should eq "é — สวัสดี 你好"
+          s.close
+        end
+      end
     end
 
     describe "#run" do

src/lua/stack/chunk.cr

@@ -13,7 +13,7 @@ module Lua
     # } # => 8
     # ```
     def run(buff : String, name : String? = nil)
-      call = CALL.new LibLua.l_loadbufferx @state, buff, buff.size, name || buff.strip, nil
+      call = CALL.new LibLua.l_loadbufferx @state, buff, buff.bytesize, name || buff.strip, nil
       raise error(call, pop) if call != CALL::OK
       call_and_return size
     end

src/lua/stack/util.cr

@@ -35,7 +35,7 @@ module Lua
     end
 
     protected def pick_results(start, finish = size)
-      elements = (start..finish).map { pop }
+      elements = (start..finish).map { pop.as(::Lua::Type) }
       elements.size > 1 ? elements : elements.first?
     end
   end