Crash when tapping on the emoji control twice fast

[mzorz]

Steps to reproduce:

1. tap on +
2. capture an image
3. tap on the stickers control very fast several times (twice is enough):

2020-07-22 09:40:36.427 15290-15290/com.automattic.portkey E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.automattic.portkey, PID: 15290
    java.lang.IllegalStateException: Fragment already added: EmojiPickerFragment{d68ef3c} (e87f460a-1a1d-4368-ae40-ab58caf66dbf)}
        at androidx.fragment.app.FragmentStore.addFragment(FragmentStore.java:67)
        at androidx.fragment.app.FragmentManager.addFragment(FragmentManager.java:1565)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:405)
        at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2169)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1992)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1947)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
        at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
2020-07-22 09:40:36.434 1797-1915/? W/EmuHWC2: validate: layer 1687 CompositionType 4, fallback

[mzorz]

Closing via #456