[Android] Avoid selection of multiple images on upload from device

[mzorz]

Inserting multiple images makes the app break for an IMAGE block.

We should force the selection to be only 1 image for now

1. start a new draft
2. insert an image block
3. select "upload from device"
4. when the screen shows pictures to choose from, tap and hold to select more than 1
5. tap OPEN
6. the app crashes

2019-01-29 18:49:16.340 22239-22239/org.wordpress.android E/AndroidRuntime: FATAL EXCEPTION: main
    Process: org.wordpress.android, PID: 22239
    java.lang.RuntimeException: Illegal callback invocation from native module. This callback type only permits a single invocation from native code.
        at com.facebook.react.bridge.CallbackImpl.invoke(CallbackImpl.java:28)
        at org.wordpress.mobile.ReactNativeGutenbergBridge.RNReactNativeGutenbergBridgeModule$2.onUploadMediaFileSelected(RNReactNativeGutenbergBridgeModule.java:105)
        at org.wordpress.mobile.WPAndroidGlue.WPAndroidGlueCode.appendUploadMediaFile(WPAndroidGlueCode.java:329)
        at org.wordpress.android.editor.GutenbergEditorFragment.appendMediaFile(GutenbergEditorFragment.java:418)
        at org.wordpress.android.ui.posts.EditPostActivity.addMediaVisualEditor(EditPostActivity.java:2712)
        at org.wordpress.android.ui.posts.EditPostActivity.access$4800(EditPostActivity.java:192)
        at org.wordpress.android.ui.posts.EditPostActivity$AddMediaListThread$3.run(EditPostActivity.java:2699)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
2019-01-29 18:49:16.347 1105-2523/? W/ActivityManager:   Force finishing activity org.wordpress.android/.ui.posts.EditPostActivity

[mzorz]

Closing via wordpress-mobile/WordPress-Android#9150