Bugfix: emojis cannot be used as filenames.

Fixes #1129.

src/androidTest/java/de/dennisguse/opentracks/util/FileUtilsTest.java

@@ -15,6 +15,8 @@
  */
 package de.dennisguse.opentracks.util;
 
+import static org.junit.Assert.assertEquals;
+
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -22,8 +24,6 @@ import org.junit.runners.JUnit4;
 import java.io.File;
 import java.util.Arrays;
 
-import static org.junit.Assert.assertEquals;
-
 /**
  * Tests for {@link FileUtils}.
  *
@@ -101,6 +101,13 @@ public class FileUtilsTest {
         assertEquals(expected, FileUtils.sanitizeFileName(name));
     }
 
+    @Test
+    public void testSanitizeFileName_emoji() {
+        String name = "\uD83C\uDF5B-Food";
+        String expected = "_-Food";
+        assertEquals(expected, FileUtils.sanitizeFileName(name));
+    }
+
     /**
      * Tests {@link FileUtils#truncateFileName(File, String, String)}.
      * Verifies the a long file name is truncated.