lazymanifest: don't crash when out of memory (issue5916)

self->lines can be NULL if we failed to allocate memory for it.

mercurial/cext/manifest.c

@@ -185,7 +185,7 b' static void lazymanifest_dealloc(lazyman'
 {
 	/* free any extra lines we had to allocate */
 	int i;
-	for (i = 0; i < self->numlines; i++) {
+	for (i = 0; self->lines && (i < self->numlines); i++) {
 		if (self->lines[i].from_malloc) {
 			free(self->lines[i].start);
 		}