Initialize more stuff in OpenALPlayer's constructor (CID #1111296)
Initialize drop when loading timecodes (CID #1111295)
Fix incorrect scope of variable in mkv_wrap.cpp

Worked by coincidence since the required value was left on the stack.

CID #1111282.
Use more make_unique

Shuts up a bunch of Coverity false-positives and might fix a true
positive or two.
Remove pointless data member (CID #739030)