Fix IndexOutOfBoundsException in aggregator function (#11113)

Signed-off-by: Anders Alfredsson <andersb86@gmail.com>

bundles/org.openhab.binding.smhi/README.md

@@ -34,6 +34,7 @@ The complete channel identifier is the channel group id (`hour_<offset>` or `day
 or the number of hours/days from now) + the channel id, concatenated with a `#`.
 
 Examples:
+
 * Temperature for the current hour: `hour_0#t`
 * Total precipitation 3 days from now: `day_3#ptotal`
 

bundles/org.openhab.binding.smhi/src/main/java/org/openhab/binding/smhi/internal/ForecastAggregator.java

@@ -64,6 +64,9 @@ public class ForecastAggregator {
      */
     public static Optional<BigDecimal> total(TimeSeries timeSeries, int dayOffset, String parameter) {
         List<Forecast> dayForecasts = timeSeries.getDay(dayOffset);
+        if (dayForecasts.size() == 1) {
+            return dayForecasts.get(0).getParameter(parameter);
+        }
         List<BigDecimal> values = new ArrayList<>();
         for (int i = 0; i < dayForecasts.size(); i++) {
             Forecast current = dayForecasts.get(i);

bundles/org.openhab.binding.smhi/src/main/java/org/openhab/binding/smhi/internal/SmhiHandler.java

@@ -254,6 +254,7 @@ public class SmhiHandler extends BaseThingHandler {
         } catch (RuntimeException e) {
             logger.warn("Unexpected exception occurred, please report to the developers: {}: {}", e.getClass(),
                     e.getMessage());
+            logger.debug("Details: ", e);
         }
     }