Fix Header.php registerFont()

registerFont() registered fonts and colors from sections, but not from subparts of sections, such as textruns.

Author: rasamassen

src/PhpWord/Writer/RTF/Part/Header.php

@@ -204,6 +204,14 @@ private function registerFont(): void
                 if (method_exists($element, 'getFontStyle')) {
                     $style = $element->getFontStyle();
                     $this->registerFontItems($style);
+                } elseif (method_exists($element, 'getElements')) { 
+                    $textRuns = $element->getElements();
+                    foreach ($textRuns as $textRun) {
+                        if (method_exists($textRun, 'getFontStyle')) {
+                            $style = $textRun->getFontStyle();
+                            $this->registerFontItems($style);
+                        }
+                    }
                 }
             }
         }