title: Invalid JSON text in argument 1 - json_contains in MySQL 5.7.8
body: <p>hello i have this 'database x6072_k2_item's with a field 'extra_fields', inside this values</p>
  
  <pre><code>[{"id":"1","value":"0000 €"},
  {"id":"2","value":" Des requins marteaux en abondance"},
  {"id":"3","value":" images/Forfaits/c6bo-voyages-plongee-croisiere-plongee-a*-l-ile-coco-avec-la-flotte-sea-hunter"},
  {"id":"4","value":""},
  {"id":"5","value":""},
  {"id":"6","value":""},
  {"id":"7","value":"Transferts inclus"},
  {"id":"8","value":""},
  {"id":"9","value":""},
  {"id":"10","value":"De décembre à*avril "},
  {"id":"11","value":"bancs de requins marteaux, raies mantas "},
  {"id":"12","value":"Niveau 2 / Advanced Open Water avec 50 plongées minimum, Deep Diver recommandé"},
  {"id":"13","value":"7"},
  {"id":"14","value":"5"},
  {"id":"15","value":"1"}]
  </code></pre>
  
  <p>i will try to find values inside this
  i do this request</p>
  
  <pre><code>SELECT * FROM `x6072_k2_items`
  where json_contains(extra_fields,'{"id":"7","Transferts inclus"}','$')=1 LIMIT 0, 25
  </code></pre>
  
  <p>but i have this error</p>
  
  <pre><code>#3141 - Invalid JSON text in argument 1 to function json_contains: "Invalid escape character in string." at position 846.
  </code></pre>
  
  <p>thanks for any help</p>