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>
diff --git a/line-log.c b/line-log.c
index b7864ad..e13455f 100644
--- a/line-log.c
+++ b/line-log.c
@@ -1099,6 +1099,7 @@
 			rg->pair = diff_filepair_dup(queue->queue[i]);
 			memcpy(&rg->diff, pairdiff, sizeof(struct diff_ranges));
 		}
+		free(pairdiff);
 	}
 
 	return changed;