[PATCH v1 1/2] lib: Fix potential invalid read past an empty string

==22884== ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60168291 at pc 0x7ff6295680e5 bp 0x7fff4ab9aa40 sp 0x7fff4ab9aa08 READ of size 1 at 0x60168291 thread T0 #0 0x7ff6295680e4 in __interceptor_strcmp ??:? #1 0x44763b in _thread_add_message /home/todd/.apps/notmuch/

[PATCH v1 1/2] lib: Fix potential invalid read past an empty string

==22884== ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60168291 at pc 0x7ff6295680e5 bp 0x7fff4ab9aa40 sp 0x7fff4ab9aa08 READ of size 1 at 0x60168291 thread T0 #0 0x7ff6295680e4 in __interceptor_strcmp ??:? #1 0x44763b in _thread_add_message /home/todd/.apps/notmuch/