Fix sample/item being out of the combined series time range

For example, if there are 24 valid pollen samples and 20 valid air
quality items, the maximum pollen sample could be de 23th, but the
resulting combined series will only cover 20 items. So, it is should not
return that, but only look in the first 20 pollen samples for the
maximum sample.

src/providers/combined.rs

@@ -81,14 +81,17 @@ fn merge(
     }
 
     // Find the maximum sample/item of each series.
-    // Note: Unwrapping is possible because each series has at least an item otherwise `.first`
+    // Note 1: Unwrapping is possible because each series has at least an item otherwise `.first`
     // would have failed above.
-    let pollen_max = pollen_samples
+    // Note 2: Ensure that the maximum sample/item is in scope of the time range covered by the
+    //   combined items.
+    let zip_len = std::cmp::min(pollen_samples.len(), aqi_items.len());
+    let pollen_max = pollen_samples[..zip_len]
         .iter()
         .max_by_key(|sample| sample.score)
         .cloned()
         .unwrap();
-    let aqi_max = aqi_items
+    let aqi_max = aqi_items[..zip_len]
         .iter()
         .max_by_key(|item| (item.value * 1_000.0) as u32)
         .cloned()
@@ -206,7 +209,7 @@ mod tests {
         let merged = super::merge(shifted_pollen_samples, aqi_items.clone());
         assert!(merged.is_some());
         let (paqi, max_pollen, max_aqi) = merged.unwrap();
-        assert_eq!(paqi, Vec::from([Item::new(t_1, 2.9), Item::new(t_2, 3.0),]));
+        assert_eq!(paqi, Vec::from([Item::new(t_1, 2.9), Item::new(t_2, 3.0)]));
         assert_eq!(max_pollen, BuienradarSample::new(t_2, 3));
         assert_eq!(max_aqi, LuchtmeetnetItem::new(t_1, 2.9));
 
@@ -222,10 +225,25 @@ mod tests {
         let merged = super::merge(pollen_samples.clone(), shifted_aqi_items);
         assert!(merged.is_some());
         let (paqi, max_pollen, max_aqi) = merged.unwrap();
-        assert_eq!(paqi, Vec::from([Item::new(t_1, 3.0), Item::new(t_2, 2.9),]));
+        assert_eq!(paqi, Vec::from([Item::new(t_1, 3.0), Item::new(t_2, 2.9)]));
         assert_eq!(max_pollen, BuienradarSample::new(t_1, 3));
         assert_eq!(max_aqi, LuchtmeetnetItem::new(t_2, 2.9));
 
+        // The maximum sample/item should not be later then the interval the PAQI items cover.
+        let merged = super::merge(pollen_samples[..3].to_vec(), aqi_items.clone());
+        assert!(merged.is_some());
+        let (paqi, max_pollen, max_aqi) = merged.unwrap();
+        assert_eq!(paqi, Vec::from([Item::new(t_0, 1.1)]));
+        assert_eq!(max_pollen, BuienradarSample::new(t_0, 1));
+        assert_eq!(max_aqi, LuchtmeetnetItem::new(t_0, 1.1));
+
+        let merged = super::merge(pollen_samples.clone(), aqi_items[..3].to_vec());
+        assert!(merged.is_some());
+        let (paqi, max_pollen, max_aqi) = merged.unwrap();
+        assert_eq!(paqi, Vec::from([Item::new(t_0, 1.1)]));
+        assert_eq!(max_pollen, BuienradarSample::new(t_0, 1));
+        assert_eq!(max_aqi, LuchtmeetnetItem::new(t_0, 1.1));
+
         // Merging fails because the samples/items are too far (6 hours) apart.
         let shifted_aqi_items = aqi_items
             .iter()