Fix crash on attempting segmented exclusion of candidate with no votes

src/stv/gregory.rs

@@ -391,16 +391,22 @@ where
 		}
 		ExclusionMethod::ByValue => {
 			// Exclude by value
-			let max_value = excluded_candidates.iter()
-				.map(|c| state.candidates[c].parcels.iter()
+			let excluded_with_votes: Vec<&&Candidate> = excluded_candidates.iter().filter(|c| !state.candidates[*c].parcels.is_empty()).collect();
+			
+			if excluded_with_votes.is_empty() {
+				votes_remain = false;
+			} else {
+				// If candidates to exclude still having votes, select only those with the greatest value
+				let max_value = excluded_with_votes.iter()
+					.map(|c| state.candidates[*c].parcels.iter()
 						.map(|p| p.iter().map(|v| &v.value / &v.ballot.orig_value).max().unwrap())
 						.max().unwrap())
 					.max().unwrap();
 				
 				votes_remain = false;
 				
-			for excluded_candidate in excluded_candidates.iter() {
-				let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
+				for excluded_candidate in excluded_with_votes.iter() {
+					let count_card = state.candidates.get_mut(*excluded_candidate).unwrap();
 					
 					// Filter out just those votes with max_value
 					let mut remaining_votes = Vec::new();
@@ -429,6 +435,7 @@ where
 					count_card.transfer(&-votes_transferred);
 				}
 			}
+		}
 		ExclusionMethod::ParcelsByOrder => {
 			// Exclude by parcel by order
 			if excluded_candidates.len() > 1 {
@@ -436,6 +443,10 @@ where
 			}
 			
 			let count_card = state.candidates.get_mut(excluded_candidates[0]).unwrap();
+			
+			if count_card.parcels.is_empty() {
+				votes_remain = false;
+			} else {
 				votes = count_card.parcels.remove(0);
 				votes_remain = !count_card.parcels.is_empty();
 				
@@ -444,6 +455,7 @@ where
 				checksum -= &votes_transferred;
 				count_card.transfer(&-votes_transferred);
 			}
+		}
 		_ => panic!()
 	}