Fix "minor" bug causing solvers to become autistic after the first search is over.

src/main/scala/leon/synthesis/SimpleSearch.scala

@@ -71,6 +71,8 @@ class SimpleSearch(synth: Synthesizer,
   var shouldStop = false
 
   def search(): Option[Solution] = {
+    sctx.solver.init()
+
     shouldStop = false
 
     while (!g.tree.isSolved && !shouldStop) {