Fix segfault on windows when setting block visibilities

This fixes a segfault on windows debug builds which occurs
when the address of the first element in an empty vector is
taken to call SetElements().

Change-Id: I4a75d22190a471899c9e93a32db3a1ec0aa819d2
Merge topic 'multi-block-color-support' into next

b9ef4e2 Fix segfault on windows when setting block visibilities