Fix crash on unknown values

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/workouts/WorkoutValueFormatter.java

@@ -40,6 +40,10 @@ public class WorkoutValueFormatter {
     }
 
     public String formatValue(final Object rawValue, String unit) {
+        if (rawValue == null) {
+            return GBApplication.getContext().getString(R.string.stats_empty_value);
+        }
+
         if (ActivitySummaryEntries.UNIT_RAW_STRING.equals(unit)) {
             return String.valueOf(rawValue);
         }
@@ -54,6 +58,10 @@ public class WorkoutValueFormatter {
             }
         }
 
+        if (!(rawValue instanceof Number)) {
+            return String.valueOf(rawValue);
+        }
+
         double value = ((Number) rawValue).doubleValue();
 
         if (!show_raw_data) {