index-pack: use streaming interface for collision test on large blobs

When putting whole objects in core is unavoidable, try match object
type and size first before actually inflating.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5300-pack-object.sh

@@ -418,4 +418,9 @@ test_expect_success \
     'test_must_fail git index-pack -o bad.idx test-3.pack 2>msg &&
      grep "SHA1 COLLISION FOUND" msg'
 
+test_expect_success \
+    'make sure index-pack detects the SHA1 collision (large blobs)' \
+    'test_must_fail git -c core.bigfilethreshold=1 index-pack -o bad.idx test-3.pack 2>msg &&
+     grep "SHA1 COLLISION FOUND" msg'
+
 test_done