Fixes #2114 (nulls in LodGenerator result)

[MelVimL]

This patch fixes 2114 and adds simple tests.

Removes the check if some lod failed.
The performance gain is negligible, most of the time it copies <10 VertexBuffer refs unless I overlook something.

[MelVimL]

Fixes #2114

[riccardobl]

The following unit tests are currently failing in this PR:
com.jme3.tools.LodGeneratorTest > testMonkeyReductionProportional
com.jme3.tools.LodGeneratorTest > testMonkeyReductionConstant
com.jme3.tools.LodGeneratorTest > testMonkeyReductionCollapsCost

This could mean that the tests need to be updated or that the PR introduces issues.

[MelVimL]

Build test failed because of 3 tests I made. Locale execution without gradle works, with gradle build it fails.
I guess the causing part is this:

URL assetCfgUrl = JmeSystem.getPlatformAssetConfigURL(); AssetManager assetManager = JmeSystem.newAssetManager(assetCfgUrl);

Error: 
F:\Programming\jmonkeyengine\jme3-plugins-json-gson\src\main\java\com\jme3\plugins\gson\GsonObject.java:81: warning: [unchecked] unchecked conversion
    Entry<String, JsonElement>[] entries = new Entry[entrySet.size()];
                                           ^

required: java.util.Map.Entry<java.lang.String,com.jme3.plugins.json.JsonElement>[]
found: java.util.Map.Entry[]
1 warning
\jmonkeyengine\jme3-plugins\src\gltf\java\com\jme3\scene\plugins\gltf\TextureTransformExtensionLoader.java:135: warning: [unchecked] unchecked conversion
Map<Integer, Matrix3f> transformMap = loader.fetchFromCache("textureTransformData", 1, HashMap.class);
^
required: java.util.Map<java.lang.Integer,com.jme3.math.Matrix3f>
found: java.util.HashMap
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
1 warning

320 tests completed, 3 failed, 1 skipped

FAILURE: Build failed with an exception.

[MelVimL]

@riccardobl I removed the Test decorator. I guess it is an issue with loading the Jaime.j3o asset while building.

[stephengold]

@riccardobl Do you support disabling the failing junit tests?

[MelVimL]

@stephengold @riccardobl I added javadoc and the licenses.

[riccardobl]

Apologies for the late reply, somehow i've missed the notifications.
These tests were added in this pr correct? In that case i have nothing against disabling them if there are technical challenges in making them work.
I think this can be merged

[MelVimL]

@riccardobl
"These tests were added in this pr correct?":
Yes.