wlr_output: remove idle_done on output destroy

If an output is destroyed while an idle_done event is scheduled, it
results in the following Address Sanitizer Output:

==1469==ERROR: AddressSanitizer: heap-use-after-free on address 0x6170000bb668 at pc 0x7f49aaa0c348 bp 0x7ffed5da35b0 sp 0x7ffed5da35a0
WRITE of size 8 at 0x6170000bb668 thread T0
    #0 0x7f49aaa0c347 in schedule_done_handle_idle_timer ../subprojects/wlroots/types/wlr_output.c:265
    #1 0x7f49aa2f875b in wl_event_loop_dispatch_idle (/usr/lib/libwayland-server.so.0+0xa75b)
    #2 0x7f49aa2f8815 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xa815)
    #3 0x7f49aa2f739b in wl_display_run (/usr/lib/libwayland-server.so.0+0x939b)
    #4 0x556622dadd51 in server_run ../sway/server.c:216
    #5 0x556622dac25d in main ../sway/main.c:397
    #6 0x7f49aa0d0ce2 in __libc_start_main (/usr/lib/libc.so.6+0x23ce2)
    #7 0x556622d8d09d in _start (/usr/local/bin/sway+0x3909d)

0x6170000bb668 is located 488 bytes inside of 672-byte region [0x6170000bb480,0x6170000bb720)
freed by thread T0 here:
    #0 0x7f49aabc8f89 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:66
    #1 0x7f49aa968fc2 in drm_connector_destroy ../subprojects/wlroots/backend/drm/drm.c:829
    #2 0x7f49aaa0cc52 in wlr_output_destroy ../subprojects/wlroots/types/wlr_output.c:357
    #3 0x7f49aa96d2e9 in scan_drm_connectors ../subprojects/wlroots/backend/drm/drm.c:1265
    #4 0x7f49aa961a59 in drm_invalidated ../subprojects/wlroots/backend/drm/backend.c:135
    #5 0x7f49aaa2e1e9 in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
    #6 0x7f49aa98319f in udev_event ../subprojects/wlroots/backend/session/session.c:52
    #7 0x7f49aa2f87f1 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xa7f1)

previously allocated by thread T0 here:
    #0 0x7f49aabc95a1 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:95
    #1 0x7f49aa96b7a2 in scan_drm_connectors ../subprojects/wlroots/backend/drm/drm.c:1114
    #2 0x7f49aa961a59 in drm_invalidated ../subprojects/wlroots/backend/drm/backend.c:135
    #3 0x7f49aaa2e1e9 in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
    #4 0x7f49aa98319f in udev_event ../subprojects/wlroots/backend/session/session.c:52
    #5 0x7f49aa2f87f1 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xa7f1)

SUMMARY: AddressSanitizer: heap-use-after-free ../subprojects/wlroots/types/wlr_output.c:265 in schedule_done_handle_idle_timer
Shadow bytes around the buggy address:
  0x0c2e8000f670: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f680: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f690: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c2e8000f6a0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c2e8000f6b0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
=>0x0c2e8000f6c0: fd fd fd fd fd fd fd fd fd fd fd fd fd[fd]fd fd
  0x0c2e8000f6d0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c2e8000f6e0: fd fd fd fd fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f6f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f700: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f710: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb

Remove the idle_done idle timer when the output is destroyed

types/wlr_output.c

@@ -350,6 +350,10 @@ void wlr_output_destroy(struct wlr_output *output) {
 		wl_event_source_remove(output->idle_frame);
 	}
 
+	if (output->idle_done != NULL) {
+		wl_event_source_remove(output->idle_done);
+	}
+
 	pixman_region32_fini(&output->pending.damage);
 	pixman_region32_fini(&output->damage);