fix: searchlink can error in the plugin check

The error occurred because of how searchLink() is called on line 49:

  if ($support = searchLink($info, $url) ?: searchLink($info, newurl($url))) {

  Here's the sequence of events that caused the issue:

  1. First call: searchLink($info, $url) - This works fine if $info contains the JSON data from
  /tmp/community.applications/tempFiles/templates.json
  2. If first call returns falsy: The ?: operator (shorthand ternary) triggers the second call:
  searchLink($info, newurl($url))
  3. The problem: When the first searchLink() returns null or false, PHP's ?: operator evaluates
  the second expression. However, if $info itself is null (which can happen if the JSON file
  doesn't exist or is empty - see line 19 where readJson() returns [] for missing files), then
  searchLink(null, newurl($url)) is called.
  4. The crash: Inside searchLink(), when $db is null, calling count($db) throws the TypeError
  because count() requires an array or Countable object, not null.

  Root causes:
  - The JSON file at /tmp/community.applications/tempFiles/templates.json might not exist or could
  be corrupted
  - The readJson() function returns an empty array [] for missing files, but if the JSON decode
  fails, it could return null
  - The code wasn't defensive against null values being passed to searchLink()

  The fix adds is_array($db) check to ensure we only attempt to count when we have a valid array.

emhttp/plugins/dynamix.plugin.manager/post-hooks/post_plugin_checks

@@ -24,7 +24,7 @@ function newurl($url) {
   return str_replace($oldURL,$newURL,$url);
 }
 function searchLink(&$db,$url) {
-  if ($url) for ($i = 0; $i < count($db); $i++) if ( ($db[$i]['PluginURL']??null)==$url) return $db[$i]['Support']??null;
+  if ($url && is_array($db)) for ($i = 0; $i < count($db); $i++) if ( ($db[$i]['PluginURL']??null)==$url) return $db[$i]['Support']??null;
 }
 
 $type    = $argv[1]??'';   // plugin or language