unprepared return value bug fixed (laravel#19667)

PDO::exec() may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE.

src/Illuminate/Database/Connection.php

@@ -490,7 +490,7 @@ public function unprepared($query)
                 return true;
             }
 
-            return (bool) $this->getPdo()->exec($query);
+            return $this->getPdo()->exec($query) === false ? false : true;
         });
     }