Fix a dereference of a null pointer

When exiting from for loop by not satisfying the condition of `(s = next[i])` at FcCacheRemoveUnlocked()
referring s->alloated will be invalid.
2 jobs for <span class="ref-name">covscan</span> in 6 minutes and 3 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build
passed #53915
shared-build

00:05:26

passed #53916
static-build

00:04:27