Fix some signed/unsigned mismatches (/W4 warnings).
Fix the remaining /W4 C4510 and C4610 warnings.
Fix the /W4 C4701 warnings: using potentially uninitialized local variable.
Use C++ style enum and struct declarations in C++ code.
Update SetThreadName based on the latest version available on MSDN.
build_lavfilters: Fix Rebuild.
VobSubFile.cpp: Use the right size specifier in Format().
Check return value.

Fixes CID #1109591
Fix uninitialized class members.

Fixes CID #966364, #966344, #966315, #966315, #966347, #966319, #966314,
 #966313, #966280