Update affected_rows after calling mysql_next_result (#1412)

Fix: #1411
Followup: #1383

When using multi statement, we need to update the affected rows
after each call to `mysql_next_result`.

Author: byroot

ext/mysql2/client.c

@@ -1282,6 +1282,7 @@ static VALUE rb_mysql_client_next_result(VALUE self)
     int ret;
     GET_CLIENT(self);
     ret = mysql_next_result(wrapper->client);
+    wrapper->affected_rows = mysql_affected_rows(wrapper->client);
     if (ret > 0) {
       rb_raise_mysql2_error(wrapper);
       return Qfalse;

spec/mysql2/client_spec.rb

@@ -1064,12 +1064,23 @@ def run_gc
     end
 
     it "#affected_rows should return a Fixnum, from the last INSERT/UPDATE" do
-      @client.query "INSERT INTO lastIdTest (blah) VALUES (1234)"
-      expect(@client.affected_rows).to eql(1)
+      @client.query "INSERT INTO lastIdTest (blah) VALUES (1234), (5678)"
+      expect(@client.affected_rows).to eql(2)
       @client.query "UPDATE lastIdTest SET blah=4321 WHERE id=1"
       expect(@client.affected_rows).to eql(1)
     end
 
+    it "#affected_rows with multi statements returns the last result's affected_rows" do
+      @client.set_server_option(Mysql2::Client::OPTION_MULTI_STATEMENTS_ON)
+
+      @client.query("INSERT INTO lastIdTest (blah) VALUES (1234), (5678); UPDATE lastIdTest SET blah=4321 WHERE id=1")
+      expect(@client.affected_rows).to eq(2)
+      expect(@client.next_result).to eq(true)
+      expect(@client.affected_rows).to eq(1)
+    ensure
+      @client.set_server_option(Mysql2::Client::OPTION_MULTI_STATEMENTS_OFF)
+    end
+
     it "#affected_rows isn't cleared by Statement#close" do
       stmt = @client.prepare("INSERT INTO lastIdTest (blah) VALUES (1234)")