Fix filename generation and add testcasce

Fixes #1169

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/FileUtils.java

@@ -318,6 +318,6 @@ public class FileUtils {
      * @return the valid file name
      */
     public static String makeValidFileName(String name) {
-        return name.replaceAll("\0/:\\r\\n\\\\", "_");
+        return name.replaceAll("[\0/:\\r\\n\\\\]", "_");
     }
 }

app/src/test/java/nodomain/freeyourgadget/gadgetbridge/test/FileUtilsTest.java

@@ -0,0 +1,19 @@
+package nodomain.freeyourgadget.gadgetbridge.test;
+
+import org.junit.Test;
+
+import nodomain.freeyourgadget.gadgetbridge.util.FileUtils;
+
+import static org.junit.Assert.assertEquals;
+
+public class FileUtilsTest extends TestBase {
+
+    @Test
+    public void testValidFileName() {
+        String tempName = "foo:bar";
+        assertEquals("foo_bar", FileUtils.makeValidFileName(tempName));
+
+        tempName = "fo\no::bar";
+        assertEquals("fo_o__bar", FileUtils.makeValidFileName(tempName));
+    }
+}