Fix sigabrt/sigsegv on shutdown

Reenable call to growlight_stop() in shutdown_cycle() of
growlight. Fix bug in adapter_free() where we needed to
check for NULL prev/next on the circular list.

Closes #106.

README.md

@@ -108,7 +108,7 @@ with `v` to see full details about the adapter (along with other information):
 │sda: Samsung SSD 8502B6Q (465.76GiB) S/N: S2RANX0H729580X WC+ WRV- RO-   │
 │Sectors: 976773168 (512B logical / 512B physical) SAT3 (6Gbps)           │
 │Partitioning: gpt I/O scheduler: [mq-deadline] none                      │
-│    512MiB P₀₁ 2048→1050623 sda1 (unnamed) ef00 1MiB align               │
+│    512MiB P₀ 2048→1050623 sda1 (unnamed) ef00 1MiB align                │
 │ 510.98MiB vfat “GRIMESESP” at /boot/efi                                 │
 ╰─────────────────────────────────────────────────────────────────────────╯
 </pre>

src/notcurses/notcurses.c

@@ -5865,13 +5865,13 @@ static void
 adapter_free(void *cv){
   adapterstate *as = cv;
   lock_notcurses_growlight();
-  as->prev->next = as->next;
-  as->next->prev = as->prev;
+  if(as->prev){
+    as->prev->next = as->next;
+    as->next->prev = as->prev;
+  }
   if(as->rb){
     ncreel_del(PR, as->rb);
   }
-  as->next->prev = as->prev;
-  as->prev->next = as->next;
   free_adapter_state(as); // clears subentries
   --count_adapters;
   draw_main_window(notcurses_stdplane(NC)); // Update the device count
@@ -5892,12 +5892,12 @@ shutdown_cycle(void){
 
   diag("User-initiated shutdown\n");
   ps = show_splash(L"Shutting down...");
-  /*if(growlight_stop()){
+  if(growlight_stop()){
     kill_splash(ps);
     notcurses_stop(NC);
     dump_diags();
     exit(EXIT_FAILURE);
-  } FIXME */
+  }
   kill_splash(ps);
   if(notcurses_stop(NC)){
     dump_diags();