Fixed backtracking matcher to work if malloc(0) returns NULL.
Fixed backtracking matcher to work if malloc(0) returns NULL.

When configured with --without-alloca, the backtracking matches uses
malloc() to allocate memory.  On some platforms, at least Digital UNIX
V4.0, trying to allocate a zero length block with malloc() gives NULL
(i.e. an error), instead of some pointer.

darcs-hash:20060521065208-ced27-f0bea9a5678cc4403f88998b477b4a1d23ba1d92.gz

laurikari/tre,laurikari/tre,amlweems/tre,amlweems/tre,laurikari/tre,amlweems/tre