Incorrect __newindex implementation

[Ayplow]

Attempting to use multiple assignment on a table with a __newindex metamethod, only the first value will be forwarded to it.

To Reproduce

In moonsharp, the following script

local MT = {}
function MT:__newindex(key, value)
  print(key, " was assigned to [", value, "]")
end
local T = {}
setmetatable(T, MT)
T.A, T.B = 1, 2

produces this output

A was assigned to [1]
B was assigned to [nil]

Expected behavior The official Lua interpreter outputs

B        was assigned to [      2       ]
A        was assigned to [      1       ]

[Joy-less]

Fix in #325