handle .jcall unexpected error

[MohammedFCIS]

Overview

When .get.desc.values method tries to evaluate a descriptor value and checks for possible exceptions using:
.jcall(dval, "Ljava/lang/Exception;", "getException"),
that line itself sometime generates NPE crashing the whole process, hence the suggested fix.

Reproduce Code

smiles <- c("CC(C)(C)NC(=O)[C@@H]1CN(CC2=CN=CC=C2)CCN1C[C@@H](O)C[C@@H](CC1=CC=CC=C1)C(=O)N[C@@H]1[C@H](O)CC2=CC=CC=C12",
"[Gd+3].CNC(=O)CN(CCN(CCN(CC([O-])=O)CC(=O)NC)CC([O-])=O)CC([O-])=O")

molecules <- rcdk::parse.smiles(smiles)

which.desc <- "org.openscience.cdk.qsar.descriptors.molecular.ChiPathDescriptor"

featurea <- eval.desc(molecules, which.desc)