Remove assert since it was crashing the mutli process driver tests. Made the code behave correctly when indexes are out of range or the collection is empty and is "log enable lldb unwind" is enabled, log an error message.
Remove assert since it was crashing the mutli process driver tests. Made the code behave correctly when indexes are out of range or the collection is empty and is "log enable lldb unwind" is enabled, log an error message.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@275226 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 65ba5d58a55a2f9d1dd35b0edab1df54e96ffb14)

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb