Cherry-pick 3194a24. rdar://99740304

    CrashTracer: com.apple.WebKit.WebContent at WebKit: WebKit::WebPage::drawPagesToPDFImpl
    https://bugs.webkit.org/show_bug.cgi?id=269881
    rdar://99740304

    Reviewed by Wenson Hsieh.

    Crash reports have been showing null derefs of `m_printContext` under
    `drawPagesToPDFImpl`. However, it is unclear exactly what results in this
    scenario, and a user reports have not been found.

    Fix by adding a null check.

    * Source/WebKit/WebProcess/WebPage/WebPage.cpp:
    (WebKit::WebPage::drawPagesToPDFImpl):

    Canonical link: https://commits.webkit.org/275149@main

Identifier: 272448.622@safari-7618-branch

Source/WebKit/WebProcess/WebPage/WebPage.cpp

@@ -6248,6 +6248,9 @@ void WebPage::drawPagesToPDFImpl(FrameIdentifier frameID, const PrintInfo& print
         } else
 #endif
         {
+            if (!m_printContext)
+                return;
+
             size_t pageCount = m_printContext->pageCount();
             for (uint32_t page = first; page < first + count; ++page) {
                 if (page >= pageCount)