Tooling Kernel: Fixed editing issue in DynamicTreeTable

Combo cells from DynamicTreeTableUIProviderBase are only editable for non-null elements.

Issue-Ref: 4133 Issue-Url: #4133

Signed-off-by: Andreas Bayha bayha@fortiss.org

org.fortiss.tooling.base/src/org/fortiss/tooling/base/annotation/valueprovider/.ratings

 AnnotationInstSpec.java b4f2ed47a8984e751e04049de5bdb3cad2c0a933 GREEN
 DerivedAnnotationValueProviderBase.java afedd21d3469127bbb20adb34c191b5c9c980f6c GREEN
-EStructuralFeatureDescriptor.java 2e14df3830d854bc1693382727b2033b23d0051c GREEN
+EStructuralFeatureDescriptor.java 9665d0d3040278243dd37591535e411a90fa63bf GREEN
 EStructuralFeatureValueProviderBase.java 287facbbce47c16d892bae82a214f64ceeef2263 GREEN
 IAnnotationValueProvider.java 08e0e5f66dc97865e9ac03e1ac646af332845e14 GREEN
 ValueProviderBase.java e4e866840845346ec99a4304048f5327c4890996 GREEN