Fixed plugin loaders trying to load plugins they aren't able to load

closes #2125

This is an API break for things implementing the PluginLoader interface.

src/pocketmine/plugin/PharPluginLoader.php

@@ -101,6 +101,11 @@ class PharPluginLoader implements PluginLoader{
 		return "/\\.phar$/i";
 	}
 
+	public function canLoadPlugin(string $path) : bool{
+		$ext = ".phar";
+		return is_file($path) and substr($path, -strlen($ext)) === $ext;
+	}
+
 	/**
 	 * @param PluginBase        $plugin
 	 * @param PluginDescription $description

src/pocketmine/plugin/PluginLoader.php

@@ -53,6 +53,15 @@ interface PluginLoader{
 	 */
 	public function getPluginFilters() : string;
 
+	/**
+	 * Returns whether this PluginLoader can load the plugin in the given path.
+	 *
+	 * @param string $path
+	 *
+	 * @return bool
+	 */
+	public function canLoadPlugin(string $path) : bool;
+
 	/**
 	 * @param Plugin $plugin
 	 *

src/pocketmine/plugin/PluginManager.php

@@ -210,6 +210,9 @@ class PluginManager{
 						continue;
 					}
 					$file = $directory . $file;
+					if(!$loader->canLoadPlugin($file)){
+						continue;
+					}
 					try{
 						$description = $loader->getPluginDescription($file);
 						if($description instanceof PluginDescription){

src/pocketmine/plugin/ScriptPluginLoader.php

@@ -124,6 +124,11 @@ class ScriptPluginLoader implements PluginLoader{
 		return "/\\.php$/i";
 	}
 
+	public function canLoadPlugin(string $path) : bool{
+		$ext = ".php";
+		return is_file($path) and substr($path, -strlen($ext)) === $ext;
+	}
+
 	/**
 	 * @param PluginBase        $plugin
 	 * @param PluginDescription $description