fix app crash on sign up (#567)

* fix app crash on sign up

* code style fix

Author: besilva

Susi/Controllers/SignUpController/SignUpVCMethods.swift

@@ -197,8 +197,9 @@ extension SignUpViewController {
 
     // Check if email is already registered or not
     func checkIfEmailAlreadyExists() {
+        guard let emailAddress = emailTextField.text else { return }
         let emailCheckParam = [
-            Client.UserKeys.CheckEmail: emailTextField.text!.lowercased() as AnyObject
+            Client.UserKeys.CheckEmail: emailAddress.lowercased() as AnyObject
         ]
         Client.sharedInstance.checkRegistration(emailCheckParam) { (exists, success) in
             DispatchQueue.main.async {

Susi/Model/Client/Convenience.swift

@@ -581,7 +581,8 @@ extension Client {
     }
 
     func checkRegistration(_ params: [String: AnyObject], _ completion: @escaping(_ emailExists: Bool?, _ success: Bool) -> Void) {
-        let url = getApiUrl(UserDefaults.standard.object(forKey: ControllerConstants.UserDefaultsKeys.ipAddress) as! String, Methods.CheckRegistration)
+        guard let ipAddress = UserDefaults.standard.object(forKey: ControllerConstants.UserDefaultsKeys.ipAddress) else { return }
+        let url = getApiUrl(ipAddress as! String, Methods.CheckRegistration)
         _ = makeRequest(url, .get, [:], parameters: params, completion: { (results, message) in
             if let _ = message {
                 completion(nil, false)