Corrected buffer overflow during automatic checkpoint in fast-import.

If we previously were using a delta but we needed to checkpoint the
current packfile and switch to a new packfile we need to throw away
the delta and compress the raw object by itself, as delta chains
cannot span non-thin packfiles.  Unfortunately the output buffer
in this case needs to grow, as the size of the compressed object
may be quite a bit larger than the size of the compressed delta.

I've also avoided recompressing the object if we are checkpointing
and we didn't use a delta.  In this case the output buffer is the
correct size and has already been populated with the right data,
we just need to close out the current packfile and open a new one.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -847,16 +847,17 @@ static int store_object(
 		if (delta) {
 			free(delta);
 			delta = NULL;
+
+			memset(&s, 0, sizeof(s));
+			deflateInit(&s, zlib_compression_level);
+			s.next_in = dat;
+			s.avail_in = datlen;
+			s.avail_out = deflateBound(&s, s.avail_in);
+			s.next_out = out = xrealloc(out, s.avail_out);
+			while (deflate(&s, Z_FINISH) == Z_OK)
+				/* nothing */;
+			deflateEnd(&s);
 		}
-		memset(&s, 0, sizeof(s));
-		deflateInit(&s, zlib_compression_level);
-		s.next_in = dat;
-		s.avail_in = datlen;
-		s.avail_out = deflateBound(&s, s.avail_in);
-		s.next_out = out;
-		while (deflate(&s, Z_FINISH) == Z_OK)
-			/* nothing */;
-		deflateEnd(&s);
 	}
 
 	e->type = type;