add try catch when parsing image tag

[ray1422]

![]() will make the app crash.

E/AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher
    Process: com.abbysyyu.diary, PID: 5017
    java.lang.IndexOutOfBoundsException: replace (5 ... 15) ends beyond length 10
        at android.text.SpannableStringBuilder.checkRange(SpannableStringBuilder.java:1090)
        at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:498)
        at android.text.SpannableStringBuilder.delete(SpannableStringBuilder.java:225)
...