Avoid SEGV if there is no latest STH (#1765)
Avoid SEGV if there is no latest STH (#1765)


gdbelvin/trillian,google/trillian,gdbelvin/trillian,Martin2112/trillian,RJPercival/trillian,AlCutter/trillian,Martin2112/trillian,Martin2112/trillian,AlCutter/trillian,gdbelvin/trillian,google/trillian,RJPercival/trillian