Prevent blank statements from being cached.

stmt.go

@@ -135,7 +135,7 @@ func (c *Conn) Prepare(cmd string, args ...interface{}) (*Stmt, error) {
 		return s, nil
 	}
 	s, err := c.prepare(cmd, args...)
-	if s != nil {
+	if s != nil && s.stmt != nil {
 		s.Cacheable = true
 	}
 	return s, err

stmt_test.go

@@ -489,3 +489,12 @@ func TestIntOnArch64(t *testing.T) {
 		assert.Equal(t, i, r, "int truncated")
 	}
 }
+
+func TestBlankQuery(t *testing.T) {
+	db := open(t)
+	defer checkClose(db, t)
+
+	s, err := db.Prepare("")
+	checkNoError(t, err, "prepare error: %s")
+	defer checkFinalize(s, t)
+}