Fix npe vunerabilities

Fortify - High - can crash the program
- [x] [BasicVertexCentricQueryBuilder](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/graphdb/query/vertex/BasicVertexCentricQueryBuilder.java#L347) - Fixed in #469 (verify)
- [ ] [EdgeSerializer](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/graphdb/database/EdgeSerializer.java#L165)
- [ ] [EdgeSerializer](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/graphdb/database/EdgeSerializer.java#L173)
- [ ] [Geoshape](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/core/attribute/Geoshape.java#L444)
- [ ] [IndexHelper](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/graphdb/util/IndexHelper.java#L58)
- [x] [QueryUtil](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/graphdb/query/QueryUtil.java#L299) - Fixed in #469 (verify)
- [x] [StandardJanusGraph](https://github.com/JanusGraph/janusgraph/blob/84ead7d/janusgraph-core/src/main/java/org/janusgraph/graphdb/database/StandardJanusGraph.java#L675) - Fixed in #469 (verify)

Start by reading the unchecked locations in EdgeSerializer.java, Geoshape.java, and IndexHelper.java, then compare the checked locations and fixes referenced in #469. Inspect each listed path for the reported null-pointer vulnerability; done means the four unchecked items are addressed and the three #469 fixes are verified.

Written by the indexing model from the issue text.