Removed errant call to memset of invalid pointer.

The removed line calls memset() using temp.buffer as its first
argument.  This is unnecessary because neither temp nor temp.buffer is
subsequently used in any reachable code path.  Furthermore, in the
probable case that sc->parent->multilayer is false, temp.buffer will
not have been allocated and its pointer will be null.  It is likely
that the author meant to initialize bitmap.buffer rather than
temp.buffer, but that is unnecessary since bitmap.buffer is allocated
with gcalloc() and thus already zero-filled.
Avoid possibly freeing null pointer.

Added check for null before freeing clipmask, since it is not
guaranteed to have been allocated in the context in which is is being
freed.
Prevent possible leak by freeing temp.buffer outside conditional.

Moved freeing temp.buffer outside of the conditional block to avoid a
potential memory leak if that condition isn't taken.

(This is admittedly an edge case and can only happen if both
sc->parent->multilayer and sc->parent->strokedfont are somehow both
true.)
Merge pull request #1102 from blipvert/fixes/27

Cleaned up pointer and memory usage in SplineCharFreeTypeRasterizeNoHints