Add a return false if category doesn't exist

If DEBUG_MODE is off, exception is not throw. False is returned instead.

bl-kernel/category.class.php

@@ -17,7 +17,11 @@ class Category {
 		} else {
 				$errorMessage = 'Category not found in database by key ['.$key.']';
 				Log::set(__METHOD__.LOG_SEP.$errorMessage);
+				if (DEBUG_MODE === true) {
 					throw new Exception($errorMessage);
+				} else {
+					return false;
+				}
 		}
 	}