Switch asserts to wl_abort
assert()s can be compiled away by #defining NDEBUG. Some build systems do this.
libwayland's assertions are inexpensive, and they protect against errors that have no recovery paths. If compiled with NDEBUG, libwayland could allow both broken library code and buggy compositor code to silently do very wrong things in difficult to debug ways.
We should really be using our wl_abort() function instead of assert(), as it can't be compiled away for non-debug builds.