ClangFormat: Remove unneeded warning

- Remove warning when .clang-format file is absent
- Remove warning when a page is nullptr in addTab function

Change-Id: I4232bc77eaac56c78707fc37aaf75b00b8af9006
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/clangformat/clangformatbaseindenter.cpp

@@ -739,6 +739,9 @@ clang::format::FormatStyle ClangFormatBaseIndenter::styleForFile() const
             Utils::FilePath filePath = filePathToCurrentSettings(
                 TextEditor::TextEditorSettings::codeStyle("Cpp")->currentPreferences());
 
+            if (!filePath.exists())
+                return qtcStyle();
+
             clang::format::FormatStyle style;
             style.Language = clang::format::FormatStyle::LK_Cpp;
             const std::error_code error