[#592] fixed a regression with TMX loading
[#592] fixed a regression with TMX loading

the visible flag is only optional in the TMX file (always present when
exported to JSON), and if not present the default value is true (with
the last change, it was set to false)

rlugojr/melonJS,gopalindians/melonJS,gopalindians/melonJS,rlugojr/melonJS,srbala/melonJS,melonjs/melonJS,MarkoIvanetic/melonJS,srbala/melonJS,gopalindians/melonJS,rlugojr/melonJS,melonjs/melonJS,MarkoIvanetic/melonJS,TukekeSoft/melonJS,TukekeSoft/melonJS,srbala/melonJS,TukekeSoft/melonJS