Fix out of bounds access

Admittidely, code isn't particularly nice but I don't see any obvious better way.
Consider len=2, h1_end underflows and hw_begin = 2.

Author: Zentrik

site/src/comparison.rs

@@ -1247,10 +1247,20 @@ impl HistoricalData {
 
         let len = pcs.len();
         let (h1_end, h2_begin) = if len % 2 == 0 {
-            (len / 2 - 2, len / 2 + 1)
+            if len / 2 < 2 {
+                (0, len / 2 + 1)
+            } else {
+                (len / 2 - 2, len / 2 + 1)
+            }
         } else {
-            (len / 2 - 1, len / 2 + 1)
+            if len / 2 < 1 {
+                (0, len / 2 + 1)
+            } else {
+                (len / 2 - 1, len / 2 + 1)
+            }
         };
+        let h2_begin = std::cmp::min(len - 1, h2_begin);
+
         let q1 = median(&pcs[..=h1_end]);
         let q3 = median(&pcs[h2_begin..]);