Fix possible segfault when creating new PG::Result

Initialize connection and typemap prior to any object allocations, to make sure valid objects are marked.

This regression was introduced in commit 5061020 while introducing write barriers.
However it is not necessary to use RB_OBJ_WRITE when the "old" object (1st argument) is not yet created or immediately after it was created.
The initial assignment can and must be done before processing the typemap as it was before the above commit.

Fixes ged#530

ext/pg_result.c

@@ -208,12 +208,16 @@ pg_new_result2(PGresult *result, VALUE rb_pgconn)
 
 	this = (t_pg_result *)xmalloc(sizeof(*this) +  sizeof(*this->fnames) * nfields);
 	this->pgresult = result;
+	/* Initialize connection and typemap prior to any object allocations,
+	 * to make sure valid objects are marked. */
+	this->connection = rb_pgconn;
+	this->typemap = pg_typemap_all_strings;
+	this->p_typemap = RTYPEDDATA_DATA( this->typemap );
 	this->nfields = -1;
 	this->tuple_hash = Qnil;
 	this->field_map = Qnil;
 	this->flags = 0;
 	self = TypedData_Wrap_Struct(rb_cPGresult, &pgresult_type, this);
-	RB_OBJ_WRITE(self, &this->connection, rb_pgconn);
 
 	if( result ){
 		t_pg_connection *p_conn = pg_get_connection(rb_pgconn);
@@ -227,8 +231,6 @@ pg_new_result2(PGresult *result, VALUE rb_pgconn)
 		this->p_typemap = RTYPEDDATA_DATA( this->typemap );
 		this->flags = p_conn->flags;
 	} else {
-		RB_OBJ_WRITE(self, &this->typemap, pg_typemap_all_strings);
-		this->p_typemap = RTYPEDDATA_DATA( this->typemap );
 		this->enc_idx = rb_locale_encindex();
 	}