Minor refactoring for tool tasks

- Don't scan for translations on initialization in TranslationPageGenerator in order to speed up startup time of ToolsRunner
- Extract checking for null / empty array of File#listFiles into a separate method
- Move single method of RuntimeUtils into Utils class

src/test/java/tools/docs/translations/TranslationPageGenerator.java

@@ -34,8 +34,6 @@ public class TranslationPageGenerator implements AutoToolTask {
     private static final int[] COLOR_1 = {12,  9, 0};
     private static final int[] COLOR_2 = { 6, 15, 6};
 
-    private final TranslationsGatherer gatherer = new TranslationsGatherer();
-
     @Override
     public String getTaskName() {
         return "updateTranslations";
@@ -43,6 +41,7 @@ public class TranslationPageGenerator implements AutoToolTask {
 
     @Override
     public void executeDefault() {
+        TranslationsGatherer gatherer = new TranslationsGatherer();
         NestedTagValue translationValuesHolder = new NestedTagValue();
 
         for (TranslationInfo translation : gatherer.getTranslationInfo()) {

src/test/java/tools/docs/translations/TranslationsGatherer.java

@@ -11,6 +11,8 @@ import java.util.List;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import static tools.utils.FileIoUtils.listFilesOrThrow;
+
 /**
  * Gathers all available translations of AuthMe.
  */
@@ -31,10 +33,7 @@ public class TranslationsGatherer {
     }
 
     private void gatherTranslations() {
-        File[] files = new File(MESSAGES_FOLDER).listFiles();
-        if (files == null) {
-            throw new IllegalStateException("Cannot read files of '" + MESSAGES_FOLDER + "'");
-        }
+        File[] files = listFilesOrThrow(new File(MESSAGES_FOLDER));
         for (File file : files) {
             String code = getLanguageCode(file.getName());
             if (code != null) {