Fix OpenTTD#10993: Crash log when font caches not initialised

See also: OpenTTD#10836

src/crashlog.cpp

@@ -177,16 +177,25 @@ void CrashLog::LogConfiguration(std::back_insert_iterator<std::string> &output_i
 			VideoDriver::GetInstance() == nullptr ? "none" : VideoDriver::GetInstance()->GetInfoString()
 	);
 
+	auto log_font = [&](FontSize fs) -> std::string {
+		FontCache *fc = FontCache::Get(fs);
+		if (fc != nullptr) {
+			return fc->GetFontName();
+		} else {
+			return "[NULL]";
+		}
+	};
+
 	fmt::format_to(output_iterator,
 			"Fonts:\n"
 			" Small:  {}\n"
 			" Medium: {}\n"
 			" Large:  {}\n"
 			" Mono:   {}\n\n",
-			FontCache::Get(FS_SMALL)->GetFontName(),
-			FontCache::Get(FS_NORMAL)->GetFontName(),
-			FontCache::Get(FS_LARGE)->GetFontName(),
-			FontCache::Get(FS_MONO)->GetFontName()
+			log_font(FS_SMALL),
+			log_font(FS_NORMAL),
+			log_font(FS_LARGE),
+			log_font(FS_MONO)
 	);
 
 	fmt::format_to(output_iterator, "AI Configuration (local: {}) (current: {}):\n", _local_company, _current_company);