Use more secure access

[feixue299]

let deduplicatedMatName = materialCountDict.filter({
                  return $0.value.map({
                    Substring($0.name) // Swift wants a Substring for some reason
                  }).contains(matName)
                })[0].key.name

to

let deduplicatedMatName = materialCountDict.filter({
                  return $0.value.map({
                    Substring($0.name) // Swift wants a Substring for some reason
                  }).contains(matName)
                }).first?.key.name

[SamusAranX]

Fixed in version 1.7.