Do not cache results of previous render

This one-liner resets the `$__content` value prior to the render loop to
ensure a cached result is not returned in the off chance that
`$template` is a falsy value.

Author: weierophinney

src/Renderer/PhpRenderer.php

@@ -491,6 +491,7 @@ public function render($nameOrModel, $values = null)
         extract($__vars);
         unset($__vars); // remove $__vars from local scope
 
+        $this->__content = '';
         while ($this->__template = array_pop($this->__templates)) {
             $this->__file = $this->resolver($this->__template);
             if (! $this->__file) {