Minor, make MSVC happy by fixing memory safety warnings

These probably are [false] alarms of MSVC but this is fixing them. I don't know if this even worth to do (or has performance issue?) and probably [{{0}}](http://stackoverflow.com/a/5434963/1414809) is better to be used on hb-ot-shape-complex-arabic-fallback.hh for initializing but actually I wanted to get more familiar with harfbuzz development. It compiles with MSVC and cygwin64 GCC and make check (Testsuite: # TOTAL: 8 # PASS:  8)