randomSAT: fixed random sat generation; satlabcxx: fixed *2bson converters

src/util/ksatModel2bson.h

@@ -13,7 +13,7 @@ namespace satlab
 template<typename = bsoncxx::builder::stream::array, typename = KSATinstance::MODEL>
 void convert(bsoncxx::builder::stream::array& builder, const KSATinstance::MODEL& model)
 {
-    builder = bsoncxx::builder::stream::array();
+    builder.clear();
     
     for(auto& lit : model)
     {

src/util/minisatResult2bson.h

@@ -18,7 +18,7 @@ void convert(bsoncxx::builder::stream::document& builder, const MinisatResult& r
     using ARRAY_BUILDER = bsoncxx::builder::stream::array;
     using DOCUMENT_BUILDER = bsoncxx::builder::stream::document;
     
-    builder = DOCUMENT_BUILDER();
+    builder.clear();
     
     ARRAY_BUILDER model;
     DOCUMENT_BUILDER stats;

src/util/minisatStats2bson.h

@@ -13,7 +13,7 @@ namespace satlab
 template<typename = bsoncxx::builder::stream::document, typename = MinisatStats>
 void convert(bsoncxx::builder::stream::document& builder, const MinisatStats& stats)
 {
-    builder = bsoncxx::builder::stream::document();
+    builder.clear();
     
     builder << "solves" << static_cast<int>(stats.getSolves())
             << "starts" << static_cast<int>(stats.getStarts())