ui-diff: close td/tr/table properly

The previous commit fixed the diff-view when two trees where specified on
the querystring (sha1/sha2) but made the generated html invalid when only
a commit sha1 is specified. This fixes it.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-diff.c

@@ -106,6 +106,8 @@ void cgit_print_diff(const char *head, const char *old_hex, const char *new_hex,
 			cgit_diff_commit(commit, filepair_cb);
 		else
 			cgit_print_error(fmt("Bad commit: %s", head));
+		html("</td></tr>");
+		html("</table>");
 		return;
 	}