Fix count() use for PHP 7.2

Author: chronon

src/Report/Html/Renderer/File.php

@@ -304,7 +304,7 @@ protected function renderSource(FileNode $node)
             $popoverTitle   = '';
 
             if (array_key_exists($i, $coverageData)) {
-                $numTests = count($coverageData[$i]);
+            $numTests = ($coverageData[$i] ? count($coverageData[$i]) : 0);
 
                 if ($coverageData[$i] === null) {
                     $trClass = ' class="warning"';