Ruleset: use MsgCollector for "no sniffs registered" error

Author: jrfnl

src/Ruleset.php

@@ -255,7 +255,7 @@ public function __construct(Config $config)
         }
 
         if ($numSniffs === 0) {
-            throw new RuntimeException('ERROR: No sniffs were registered');
+            $this->msgCache->add('No sniffs were registered.', MsgCollector::ERROR);
         }
 
         $this->displayCachedMessages();

tests/Core/Ruleset/ConstructorTest.php

@@ -282,7 +282,7 @@ public function testNoSniffsRegisteredException()
         $standard = __DIR__.'/ConstructorNoSniffsTest.xml';
         $config   = new ConfigDouble(["--standard=$standard"]);
 
-        $message = 'ERROR: No sniffs were registered';
+        $message = 'ERROR: No sniffs were registered.'.PHP_EOL.PHP_EOL;
         $this->expectRuntimeExceptionMessage($message);
 
         new Ruleset($config);