bloom: clear each bloom_key after use

fill_bloom_key() allocates memory into bloom_key, we need to clean that
up once the key is no longer needed.

This fixes the following leak which was found while running t0002-t0099.
Although this leak is happening in code being called from a test-helper,
the same code is also used in various locations around git, and could
presumably happen during normal usage too.

Direct leak of 308 byte(s) in 11 object(s) allocated from:
    #0 0x49a5e2 in calloc ../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:154:3
    #1 0x6f4032 in xcalloc wrapper.c:140:8
    #2 0x4f2905 in fill_bloom_key bloom.c:137:28
    #3 0x4f34c1 in get_or_compute_bloom_filter bloom.c:284:4
    #4 0x4cb484 in get_bloom_filter_for_commit t/helper/test-bloom.c:43:11
    #5 0x4cb072 in cmd__bloom t/helper/test-bloom.c:97:3
    #6 0x4ca7ef in cmd_main t/helper/test-tool.c:121:11
    #7 0x4caace in main common-main.c:52:11
    #8 0x7f798af95349 in __libc_start_main (/lib64/libc.so.6+0x24349)

SUMMARY: AddressSanitizer: 308 byte(s) leaked in 11 allocation(s).

Signed-off-by: Andrzej Hunt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

bloom.c

@@ -283,6 +283,7 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
 			struct bloom_key key;
 			fill_bloom_key(e->path, strlen(e->path), &key, settings);
 			add_key_to_filter(&key, filter, settings);
+			clear_bloom_key(&key);
 		}
 
 	cleanup: