Make a hack to convert-cache for missing author dates in old

archives (notably the old sparse one).

Very hacky. But hopefully we can do the conversion once, and never
worry about this ever again.

convert-cache.c

@@ -233,6 +233,13 @@ static int convert_date_line(char *dst, void **buf, unsigned long *sp)
 		return len + datelen;
 	}
 
+	/*
+	 * Hacky hacky: one of the sparse old-style commits does not have
+	 * any date at all, but we can fake it by using the committer date.
+	 */
+	if (*date == '\n' && strchr(next, '>'))
+		date = strchr(next, '>')+2;
+
 	return len + sprintf(dst, "%lu -0700\n", parse_oldstyle_date(date));
 }