Fix: create zip without multimedia

Author: Andyporras

app/src/main/java/net/osmtracker/gpx/ZipHelper.java

@@ -36,6 +36,13 @@ public static File zipCacheFiles(Context context, long trackId, File fileGPX) {
         try (FileOutputStream fos = new FileOutputStream(zipFile);
              ZipOutputStream zos = new ZipOutputStream(fos)) {
 
+            // Add gpx file
+            addFileToZip(fileGPX, zos);
+
+            if(!traceFilesDirectory.exists()){
+                return zipFile;
+            }
+
             for (File multimediaFile : Objects.requireNonNull(traceFilesDirectory.listFiles())) {
                 if (!multimediaFile.isDirectory()) { // Avoid adding empty folders
                     // only add files that are not .zip files
@@ -49,9 +56,6 @@ public static File zipCacheFiles(Context context, long trackId, File fileGPX) {
                 }
             }
 
-            // Adds the original gpx file
-            addFileToZip(fileGPX, zos);
-
             Log.d(TAG, "ZIP file created: " + zipFile.getAbsolutePath());
             return zipFile;
 
@@ -87,4 +91,4 @@ private static void addFileToZip(File file, ZipOutputStream zos) throws IOExcept
             zos.closeEntry();
         }
     }
-}
+}