Fix NPE while making the screenshot bitmap mutable

[nkming2]

sCalibrationImage is null at this point, causing NPE when invoking getConfig()

stack trace:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.Bitmap$Config android.graphics.Bitmap.getConfig()' on a null object reference
	at com.kamron.pogoiv.activities.OcrCalibrationResultActivity.startCalibration(OcrCalibrationResultActivity.java:108)
	at com.kamron.pogoiv.ScreenShotHelper$1.onChange(ScreenShotHelper.java:81)
	at android.database.ContentObserver.onChange(ContentObserver.java:145)
	at android.database.ContentObserver$NotificationRunnable.run(ContentObserver.java:216)
	at android.os.Handler.handleCallback(Handler.java:789)
	at android.os.Handler.dispatchMessage(Handler.java:98)
	at android.os.Looper.loop(Looper.java:164)
	at android.app.ActivityThread.main(ActivityThread.java:6809)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

[thearaks]

The problem can be solved way more easily, see the comments for details.
Thanks for the contribution!

[thearaks]

This check is useless since the copy can't return a null bitmap.
Please remove this added lines since they're not helpful.

[nkming2]

It could be NULL according to the reference:

If the conversion is not supported, or the allocator fails, then this returns NULL

but yea, I think it's a pretty rare case and maybe just doesn't worth bothering at all

[thearaks]

Please replace this line with this instead:

sCalibrationImage = bitmap.copy(bitmap.getConfig(), true);

[nkming2]

That's also what I thought originally but I checked the reference and realized getConfig() could actually return NULL.

If the bitmap's internal config is in one of the public formats, return that config, otherwise return null.

Maybe I just make an if there

[thearaks]

Using Bitmap.Config.ARGB_8888 might be a waste of space if the screenshot bitmap used a lower color configuration.
See the previous suggestion to copy the configuration from the screenshot bitmap.

[nkming2]

Amended