Exclude XML Resources from being processed by RibbonizerTask

[mannodermaus]

Right now, RibbonizerTask fails with an NPE when trying to apply filters to a non-image resource, such as Android O's <adaptive-icon> resources:

Stack Trace

[ribbonizeLocalDebug] process /workspace/gradle-android-ribbonizer-plugin/example-custom/src/main/res/drawable-hdpi/ic_launcher.png
[ribbonizeLocalDebug] process /workspace/gradle-android-ribbonizer-plugin/example-custom/src/main/res/drawable-mdpi/ic_launcher.png
[ribbonizeLocalDebug] process /workspace/gradle-android-ribbonizer-plugin/example-custom/src/main/res/drawable-xhdpi/ic_launcher.png
[ribbonizeLocalDebug] process /workspace/gradle-android-ribbonizer-plugin/example-custom/src/main/res/drawable-xxhdpi/ic_launcher.png
[ribbonizeLocalDebug] process /workspace/gradle-android-ribbonizer-plugin/example-custom/src/main/res/mipmap-anydpi-v26/ic_launcher.xml
:example-custom:ribbonizeLocalDebug FAILED

* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':example-custom:ribbonizeLocalDebug'.
	at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:69)
	at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:46)
        ...
Caused by: java.lang.NullPointerException
	at com.github.gfx.ribbonizer.filter.ColorRibbonFilter.accept(ColorRibbonFilter.java:52)
	at com.github.gfx.ribbonizer.filter.ColorRibbonFilter.accept(ColorRibbonFilter.java:10)
	at com.github.gfx.ribbonizer.plugin.Ribbonizer$1.accept(Ribbonizer.java:35)
	at com.github.gfx.ribbonizer.plugin.Ribbonizer$1.accept(Ribbonizer.java:32)
	at com.github.gfx.ribbonizer.plugin.Ribbonizer.process(Ribbonizer.java:32)
        ...

Typically, this kind of "new launcher icon" is implemented inside of resource directories specific to -v26, but keeping the same name as pre-O resources. Therefore, when the launcher icon is normally named mipmap-<dpi>/ic_launcher.png, and then overridden on Android O with the adaptive icon at mipmap-anydpi-v26/ic_launcher.xml, ImageIO can't extract a BufferedImage out of that file and fails later on.

I've put a lot of thought into how Ribbonizer would be able to add ribbons to XML resources automatically, but to no avail. Ideally, that solution would also include <vector>/SVG resources.

For now, we should simply exclude XML altogether, though, in order to prevent people from using Ribbonizer after upgrading their app to Android O.

[gfx]

Nice catch. Thanks.

[gfx]

This is included in v2.0.0; synchronizing to jcenter might take a frew hours.

[lksnmnn]

I am getting this exact error. Without changing anything specific imho.

#31