fix Bytearray from table constructor

dev/tests/bytearray.lua

@@ -25,3 +25,6 @@ end
 print(#arr, arr:get_capacity())
 arr:trim()
 assert(#arr == arr:get_capacity())
+
+arr = Bytearray({0, 2, 7, 1, 16, 75, 25})
+assert(arr[6] == 75)

res/modules/internal/bytearray.lua

@@ -179,7 +179,7 @@ local FFIBytearray = {
             return bytearray_type(buffer, #n, #n)
         elseif t == "table" then
             local capacity = math.max(#n, MIN_CAPACITY)
-            local buffer = malloc(capacity)
+            local buffer = FFI.cast("unsigned char*", malloc(capacity))
             for i=1,#n do
                 buffer[i - 1] = n[i]
             end