fix alert criteria parsing if only a single quoted phrase

was adding a space to the front because explode was always returning an
array with one entry.

classes/Utility/Alert.php

@@ -104,7 +104,10 @@ public static function prettifyCriteria($alert_criteria, $as_parts = false) {
                 $alert_criteria = trim(preg_replace('/ +/', ' ', str_replace($phrases[0], "", $alert_criteria)));
 
                 # and then create an array with the words and phrases
-                $criteria = explode(' ', $alert_criteria);
+                $criteria = [];
+                if ( $alert_criteria != "") {
+                    $criteria = explode(' ', $alert_criteria);
+                }
                 $criteria = array_merge($criteria, $phrases[1]);
             } else {
                 $criteria = explode(' ', $alert_criteria);