Suppress non-critical PHP errors

The previous code contained various pieces that PHP usually executes
without complaints, but on some PHP installations it emits warnings.
This adds more checks that pretty much do what PHP would do anyway, but
without generating any errors.

gen.php

@@ -1,8 +1,8 @@
 <?php
 
-$type = $_POST['type'];
-$def = $_POST['def'];
-$private = $_POST['private'] ? 1 : 0;
+$type = isset($_POST['type']) ? $_POST['type'] : NULL;
+$def = isset($_POST['def']) ? $_POST['def'] : NULL;
+$private = isset($_POST['private']) ? ($_POST['private'] ? 1 : 0) : 0;
 
 if ($type != 'graph' && $type != 'digraph')
 	die("Nuh-uh. Use one of the checkboxes.");
@@ -20,6 +20,7 @@ function get_one($q)
 {
 	$res = mysql_query($q);
 	if (!$res) die("Failed to get stuff from database. Sorry!");
+	if (mysql_num_rows($res) == 0) return NULL;
 	return mysql_result($res, 0);
 }
 function id_shorten($id)

get.php

@@ -16,7 +16,7 @@ function id_lengthen($id)
 	return $res;
 }
 
-$id = $_GET['id'];
+$id = isset($_GET['id']) ? $_GET['id'] : NULL;
 if (!$id) die("No ID given.");
 if (strlen($id) == 40)
 	$q = "graph_code = '".mysql_real_escape_string($id)."'";

index.php

@@ -17,7 +17,7 @@
 <p>Definition (without the surrounding <code>[di]graph {}</code> thing): (<a
 href="http://en.wikipedia.org/wiki/DOT_language">syntax</a>, <a
 href="index.php?example=1">example</a>)<br>
-<textarea name="def" rows="20" cols="50"><?php if ($_GET['example']):
+<textarea name="def" rows="20" cols="50"><?php if (isset($_GET['example']) && $_GET['example']):
 ?>Sleep -&gt; Work [label="zombie"]
 Work -&gt; TV [label="zombie"]
 TV -&gt; Sleep [label="zombie"]