Save affected_rows on the wrapper when reading results (#1383)

Between fetching the result and accessing the affected_rows property, GC
might have been triggered and might have freed some Mysql2::Statement
objects. This calls mysql_stmt_close which resets the connection
affected_rows to -1, which in turn is treated as an error when calling
mysql_affected_rows.

```
client.query("SELECT 1")
client.affected_rows # raises Mysql2::Error
```

Note that the data type of mysql_affected_rows changed from my_ulonglong
to uint64_t starting with MySQL 8.0. Older versions should still work, though.

ext/mysql2/client.c

@@ -411,6 +411,7 @@ static VALUE allocate(VALUE klass) {
   wrapper->initialized = 0; /* will be set true after calling mysql_init */
   wrapper->closed = 1; /* will be set false after calling mysql_real_connect */
   wrapper->refcount = 1;
+  wrapper->affected_rows = -1;
   wrapper->client = (MYSQL*)xmalloc(sizeof(MYSQL));
 
   return obj;
@@ -669,6 +670,7 @@ static VALUE rb_mysql_client_async_result(VALUE self) {
     wrapper->active_fiber = Qnil;
     rb_raise_mysql2_error(wrapper);
   }
+  wrapper->affected_rows = mysql_affected_rows(wrapper->client);
 
   is_streaming = rb_hash_aref(rb_ivar_get(self, intern_current_query_options), sym_stream);
   if (is_streaming == Qtrue) {
@@ -1155,12 +1157,12 @@ static VALUE rb_mysql_client_session_track(VALUE self, VALUE type) {
  * if it was an UPDATE, DELETE, or INSERT.
  */
 static VALUE rb_mysql_client_affected_rows(VALUE self) {
-  my_ulonglong retVal;
+  uint64_t retVal;
   GET_CLIENT(self);
 
   REQUIRE_CONNECTED(wrapper);
-  retVal = mysql_affected_rows(wrapper->client);
-  if (retVal == (my_ulonglong)-1) {
+  retVal = wrapper->affected_rows;
+  if (retVal == (uint64_t)-1) {
     rb_raise_mysql2_error(wrapper);
   }
   return ULL2NUM(retVal);

ext/mysql2/client.h

@@ -12,6 +12,7 @@ typedef struct {
   int initialized;
   int refcount;
   int closed;
+  uint64_t affected_rows;
   MYSQL *client;
 } mysql_client_wrapper;
 

spec/mysql2/client_spec.rb

@@ -1033,7 +1033,7 @@ def run_gc
       expect(@client).to respond_to(:last_id)
     end
 
-    it "#last_id should return a Fixnum, the from the last INSERT/UPDATE" do
+    it "#last_id should return a Fixnum, from the last INSERT/UPDATE" do
       expect(@client.last_id).to eql(0)
       @client.query "INSERT INTO lastIdTest (blah) VALUES (1234)"
       expect(@client.last_id).to eql(1)
@@ -1043,13 +1043,6 @@ def run_gc
       expect(@client).to respond_to(:last_id)
     end
 
-    it "#last_id should return a Fixnum, the from the last INSERT/UPDATE" do
-      @client.query "INSERT INTO lastIdTest (blah) VALUES (1234)"
-      expect(@client.affected_rows).to eql(1)
-      @client.query "UPDATE lastIdTest SET blah=4321 WHERE id=1"
-      expect(@client.affected_rows).to eql(1)
-    end
-
     it "#last_id should handle BIGINT auto-increment ids above 32 bits" do
       # The id column type must be BIGINT. Surprise: INT(x) is limited to 32-bits for all values of x.
       # Insert a row with a given ID, this should raise the auto-increment state
@@ -1058,6 +1051,35 @@ def run_gc
       @client.query "INSERT INTO lastIdTest (blah) VALUES (5001)"
       expect(@client.last_id).to eql(5000000001)
     end
+
+    it "#last_id isn't cleared by Statement#close" do
+      stmt = @client.prepare("INSERT INTO lastIdTest (blah) VALUES (1234)")
+
+      @client.query "INSERT INTO lastIdTest (blah) VALUES (1234)"
+      expect(@client.last_id).to eql(1)
+
+      stmt.close
+
+      expect(@client.last_id).to eql(1)
+    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 "UPDATE lastIdTest SET blah=4321 WHERE id=1"
+      expect(@client.affected_rows).to eql(1)
+    end
+
+    it "#affected_rows isn't cleared by Statement#close" do
+      stmt = @client.prepare("INSERT INTO lastIdTest (blah) VALUES (1234)")
+
+      @client.query "INSERT INTO lastIdTest (blah) VALUES (1234)"
+      expect(@client.affected_rows).to eql(1)
+
+      stmt.close
+
+      expect(@client.affected_rows).to eql(1)
+    end
   end
 
   it "should respond to #thread_id" do