Fix problem with lazy call to typeToSort

src/main/scala/leon/FairZ3Solver.scala

@@ -978,6 +978,7 @@ class FairZ3Solver(reporter: Reporter) extends Solver(reporter) with AbstractZ3S
           case errorType => scala.sys.error("Unexpected type for singleton map: " + (ex, errorType))
         }
         case e @ EmptyMap(fromType, toType) => {
+          typeToSort(e.getType) //had to add this here because the mapRangeNoneConstructors was not yet constructed...
           val fromSort = typeToSort(fromType)
           val toSort = typeToSort(toType)
           z3.mkConstArray(fromSort, mapRangeNoneConstructors(toType)())