uuid: fix 1 byte stack overflow

scanf requires that '[' convertion specifiers have enough room for all
characters in the string, _plus a terminating null byte_. We were
previously not providing room for the terminating null byte.

This was detected by AddressSanitizer:

==15036==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffe4e774401 at pc 0x7fd33f572c98 bp 0x7ffe4e774270 sp 0x7ffe4e7739f8
WRITE of size 2 at 0x7ffe4e774401 thread T0
    #0 0x7fd33f572c97 in scanf_common /build/gcc-multilib/src/gcc-5-20160209/libsanitizer/sanitizer_common/sanitizer_common_interceptors_format.inc:340
    #1 0x7fd33f5739ea in __interceptor_vsscanf /build/gcc-multilib/src/gcc-5-20160209/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:769
    #2 0x7fd33f573b49 in __interceptor_sscanf /build/gcc-multilib/src/gcc-5-20160209/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:793
    #3 0x650db5 in is_base_uuid128 lib/uuid.c:191
    #4 0x65196e in bt_string_to_uuid lib/uuid.c:267
    #5 0x56f28e in parse_uuid src/gatt-database.c:1473
    #6 0x5729e0 in database_add_service src/gatt-database.c:2053
    #7 0x57329f in database_add_app src/gatt-database.c:2106
    #8 0x573adc in client_ready_cb src/gatt-database.c:2211
    #9 0x6695fd in get_managed_objects_reply gdbus/client.c:1097
    #10 0x7fd33efd5391  (/usr/lib/libdbus-1.so.3+0x13391)
    #11 0x7fd33efd8db0 in dbus_connection_dispatch (/usr/lib/libdbus-1.so.3+0x16db0)
    #12 0x651ecd in message_dispatch gdbus/mainloop.c:72
    #13 0x7fd33f25cc39 in g_main_context_dispatch (/usr/lib/libglib-2.0.so.0+0x49c39)
    #14 0x7fd33f25cfdf  (/usr/lib/libglib-2.0.so.0+0x49fdf)
    #15 0x7fd33f25d301 in g_main_loop_run (/usr/lib/libglib-2.0.so.0+0x4a301)
    #16 0x54b7d1 in main src/main.c:687
    #17 0x7fd33d90870f in __libc_start_main (/usr/lib/libc.so.6+0x2070f)
    #18 0x40bba8 in _start (/home/cody/g/bluez/src/bluetoothd+0x40bba8)

Address 0x7ffe4e774401 is located in stack of thread T0 at offset 33 in frame
    #0 0x650ccd in is_base_uuid128 lib/uuid.c:184

  This frame has 2 object(s):
    [32, 33) 'dummy' <== Memory access at offset 33 overflows this variable
    [96, 98) 'uuid'
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /build/gcc-multilib/src/gcc-5-20160209/libsanitizer/sanitizer_common/sanitizer_common_interceptors_format.inc:340 scanf_common
Shadow bytes around the buggy address:
  0x100049ce6830: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100049ce6840: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100049ce6850: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100049ce6860: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100049ce6870: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
=>0x100049ce6880:[01]f4 f4 f4 f2 f2 f2 f2 02 f4 f4 f4 f3 f3 f3 f3
  0x100049ce6890: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x100049ce68a0: 00 f4 f4 f4 f2 f2 f2 f2 00 00 04 f4 f2 f2 f2 f2
  0x100049ce68b0: 00 00 00 00 00 00 00 00 00 f4 f4 f4 f3 f3 f3 f3
  0x100049ce68c0: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x100049ce68d0: 01 f4 f4 f4 f2 f2 f2 f2 00 00 04 f4 f3 f3 f3 f3
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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==15036==ABORTING

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/uuid.c b/lib/uuid.c
index 20b67d037..ac071fa3f 100644
--- a/lib/uuid.c
+++ b/lib/uuid.c
@@ -183,14 +183,14 @@ static inline int is_uuid128(const char *string)
 static inline int is_base_uuid128(const char *string)
 {
 	uint16_t uuid;
-	char dummy;
+	char dummy[2];
 
 	if (!is_uuid128(string))
 		return 0;
 
 	return sscanf(string,
 		"0000%04hx-0000-1000-8000-00805%1[fF]9%1[bB]34%1[fF]%1[bB]",
-		&uuid, &dummy, &dummy, &dummy, &dummy) == 5;
+		&uuid, dummy, dummy, dummy, dummy) == 5;
 }
 
 static inline int is_uuid32(const char *string)