Making importing a single file easier (Issue #5508) (#5513)

* Added condition: if only one entry is imported, it automatically selects said entry, making importing single files easier, referring to Isse #5508

* trying Platform.runLater around the if-statement, also tried around everything in 'initialize', including and excluding the if-statement

* reverted the last change and added a comment as to why the code is there

* fixed a mistake, where 2 returns where present, where one was not necessary

src/main/java/org/jabref/gui/importer/ImportEntriesDialog.java

@@ -119,6 +119,14 @@ private void initialize() {
                         }
                     }).executeWith(Globals.TASK_EXECUTOR);
 
+                    /*
+                    inserted the if-statement here, since a Platforn.runLater() call did not work.
+                    also tried to move it to the end of the initialize method, but it did not select the entry.
+                    */
+                    if (entriesListView.getItems().size() == 1) {
+                        selectAllNewEntries();
+                      }
+
                     return container;
                 })
                 .withOnMouseClickedEvent((entry, event) -> entriesListView.getCheckModel().toggleCheckState(entry))