Added UI test reproducing NullPointerException inside DrawableMatcher

[k4k7us23]

• In my project I am using DrawableMatcher to find an ImageView by drawable inside it
• I discovered that DrawableMatcher fails with NullPointerException, in case view hierarchy contains an ImageView without any Drawable inside
• This PR adds EmptyDrawableMatcherTest, that reproduces scenario described above
• EmptyDrawableMatcherTest is marked with ignore annotation, as DrawableMatcher will be fixed in a separate PR

[Unlimity]

Good catch! Although given the fact that no one noticed and reported it before means this case is super rare

[Vacxe]

@k4k7us23 thanks for the contribution. Will create a new release ASAP.

[Vacxe]

@k4k7us23 any ETA for the fix or you wanna delegate fix to me?

[Vacxe]

Ref: #144

[k4k7us23]

@Vacxe I am planning to make a fix at the end of this week. Feel free to fix it yourself, if it's urgent

[Vacxe]

@k4k7us23 thank mate, appreciate. Please create a PR when you have a chance 😉 looking forward to it!