message: fix(login): disable login button when Username or Password or both are empty
  PR close
diff: [(ngModel)]="username"
  [placeholder]="'AUTH.USERNAME' | translate"
  autofocus
  + minlength="1"
  required
  #usernameControl="ngModel"
  />
  name="password"
  [(ngModel)]="password"
  [placeholder]="'AUTH.PASSWORD' | translate"
  + minlength="1"
  required
  #passwordControl="ngModel"
  />
  mat-button
  color="primary"
  type="submit"
  - [disabled]="
  - (passwordControl.invalid && !passwordControl.pristine) ||
  - (usernameControl.invalid && !usernameControl.pristine)
  - "
  + [disabled]="passwordControl.invalid || usernameControl.invalid"
  >
  {{ 'AUTH.LOGIN' | translate }}
  </button>
  