Handle iTunes single-number duration format

Apple says this [1] about the `<itunes:duration>` tag:

    If you specify a single number as a value (without colons), Apple
    Podcasts displays the value as seconds.

This commit makes it also handle this single-number format.

Closes: #3024

[1]: https://help.apple.com/itc/podcasts_connect/#/itcb54353390

core/src/main/java/de/danoeh/antennapod/core/syndication/parsers/DurationParser.java

@@ -8,7 +8,9 @@ public class DurationParser {
     public static long inMillis(String durationStr) throws NumberFormatException {
         String[] parts = durationStr.trim().split(":");
 
-        if (parts.length == 2) {
+        if (parts.length == 1) {
+            return toMillis(parts[0]);
+        } else if (parts.length == 2) {
             return toMillis("0", parts[0], parts[1]);
         } else if (parts.length == 3) {
             return toMillis(parts[0], parts[1], parts[2]);

core/src/test/java/de/danoeh/antennapod/core/syndication/parsers/DurationParserTest.java

@@ -16,6 +16,13 @@ public class DurationParserTest {
         assertEquals(45 * seconds, duration);
     }
 
+    @Test
+    public void testSingleNumberDurationInMillis() {
+        int twoHoursInSeconds = 2 * 60 * 60;
+        long duration = DurationParser.inMillis(String.valueOf(twoHoursInSeconds));
+        assertEquals(2 * hours, duration);
+    }
+
     @Test
     public void testMinuteSecondDurationInMillis() {
         long duration = DurationParser.inMillis("05:10");