fix orderedtable enlarge proc. (#5937)

This fixes issue #5917

tests/stdlib/torderedtable.nim

@@ -0,0 +1,18 @@
+import tables, random
+var t = initOrderedTable[int,string]()
+
+# this tests issue #5917
+var data = newSeq[int]()
+for i in 0..<1000:
+  var x = random(1000)
+  if x notin t: data.add(x)
+  t[x] = "meh"
+
+# this checks that keys are re-inserted
+# in order when table is enlarged.
+var i = 0
+for k, v in t:
+  doAssert(k == data[i])
+  doAssert(v == "meh")
+  inc(i)
+