Fix a few valgrind errors

src/config.c

@@ -436,7 +436,7 @@ int git_config_get_bool(int *out, git_config *cfg, const char *name)
 int git_config_get_string(const char **out, git_config *cfg, const char *name)
 {
 	int ret;
-	const char *str;
+	const char *str = NULL;
 
 	if ((ret = get_string(&str, cfg, name)) < 0)
 		return ret;

src/index.c

@@ -1098,7 +1098,8 @@ static int read_reuc(git_index *index, const char *buffer, size_t size)
 	size_t len;
 	int i;
 
-	if (git_vector_init(&index->reuc, 16, reuc_cmp) < 0)
+	/* This gets called multiple times, the vector might already be initialized */
+	if (index->reuc._alloc_size == 0 && git_vector_init(&index->reuc, 16, reuc_cmp) < 0)
 		return -1;
 
 	while (size) {

src/transports/local.c

@@ -227,6 +227,8 @@ static int local_negotiate_fetch(
 			git_oid_cpy(&rhead->loid, git_object_id(obj));
 		else if (error != GIT_ENOTFOUND)
 			return error;
+		else
+			memset(&rhead->loid, 0, sizeof(git_oid));
 		git_object_free(obj);
 		giterr_clear();
 	}