Fixing extraneous semicolon in jsgen output

jsgen was producing javascript objects like this
```
{, name:"foo"}
```
causing syntax errors in javascript interpretors.

compiler/jsgen.nim

@@ -1431,7 +1431,7 @@ proc genObjConstr(p: PProc, n: PNode, r: var TCompRes) =
   r.res = toRope("{")
   r.kind = resExpr
   for i in countup(1, sonsLen(n) - 1):
-    if i > 0: app(r.res, ", ")
+    if i > 1: app(r.res, ", ")
     var it = n.sons[i]
     internalAssert it.kind == nkExprColonExpr
     gen(p, it.sons[1], a)

tests/js/testobjs.nim

@@ -0,0 +1,34 @@
+## Tests javascript object generation
+
+type
+  Kg = distinct float
+  Price = int
+  Item = object of RootObj
+    weight: Kg
+    price: Price
+    desc: cstring
+  Person = object of RootObj
+    name: cstring
+    age: int
+    item: Item
+  Test = object
+    name: cstring
+  Recurse[T] = object
+    data: T
+    next: ref Recurse[T]
+
+var
+  test = Test(name: "Jorden")
+  sword = Item(desc: "pointy", weight: Kg(10.0),
+                price: Price(50))
+  knight = Person(name: "robert", age: 19, item: sword)
+  recurse4 = (ref Recurse[int])(data: 4, next: nil)
+  recurse3 = (ref Recurse[int])(data: 3, next: recurse4)
+  recurse2 = (ref Recurse[int])(data: 2, next: recurse3)
+  recurse1 = Recurse[int](data: 1, next: recurse2)
+
+
+assert(test.name == "Jorden")
+assert(knight.age == 19)
+assert(knight.item.price == 50)
+assert(recurse1.next.next.data == 3)