sparse-index: fix uninitialized jump

While testing the sparse-index, I verified a test with --valgrind and it
complained about an uninitialized value being used in a jump in the
path_matches_pattern_list() method. The line was this one:

	if (*dtype == DT_UNKNOWN)

In the call stack, the culprit was the initialization of the dtype
variable in convert_to_sparse_rec().

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sparse-index.c

@@ -34,7 +34,7 @@ static int convert_to_sparse_rec(struct index_state *istate,
 	int i, can_convert = 1;
 	int start_converted = num_converted;
 	enum pattern_match_result match;
-	int dtype;
+	int dtype = DT_UNKNOWN;
 	struct strbuf child_path = STRBUF_INIT;
 	struct pattern_list *pl = istate->sparse_checkout_patterns;