fixed source root detection for java files in default package (IDEA-74616)

java/java-tests/testData/ide/sourceRootDetection/defaultPackageWithImport/src/MyClass.java

@@ -0,0 +1,9 @@
+import java.util.*;
+//aaa
+import java.io.OutputStream;
+
+/**
+ * my class
+ */
+public class MyClass {
+}