Allocate enough memory for the terminator in commit parsing

Also allow space for the null-terminator when allocating the buffer in
packfile_unpack_compressed. Up to now, the last newline had served as
a terminator, but 858ef372 searches for a double-newline and exposes
the problem.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>

src/odb_pack.c

@@ -1246,7 +1246,8 @@ static int packfile_unpack_compressed(
 	z_stream stream;
 	unsigned char *buffer, *in;
 
-	buffer = git__malloc(size);
+	buffer = git__malloc(size + 1);
+	memset(buffer, 0x0, size + 1);
 
 	memset(&stream, 0, sizeof(stream));
 	stream.next_out = buffer;