Fix UBSAN warning about applying zero offset to null pointer

[Girgias]

vpath may be NULL here so check for it before trying to add 0 (the length of the vpath) to it.

[nielsdos]

Makes sense to me. Ig we could move the variable definition of const char *vpath = client->request.vpath; out of the if body and then check for vpath in the condition instead. However, the compiler should be smart enough to do that optimisation itself.

[Girgias]

Makes sense to me. Ig we could move the variable definition of const char *vpath = client->request.vpath; out of the if body and then check for vpath in the condition instead. However, the compiler should be smart enough to do that optimisation itself.

I suppose, but I think it was scoped to support C89 compilers prior to us moving to C99, but yeah hopefully the compiler is smart enough to do this. :)