line-log.c: fix a memleak

The `filepair` is assigned new memory with any iteration via
process_diff_filepair, so free it before the current iteration ends.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

line-log.c

@@ -1099,6 +1099,7 @@ static int process_all_files(struct line_log_data **range_out,
 			rg->pair = diff_filepair_dup(queue->queue[i]);
 			memcpy(&rg->diff, pairdiff, sizeof(struct diff_ranges));
 		}
+		free(pairdiff);
 	}
 
 	return changed;