better bounds checking for replaceSubrange

Sources/RelativeCollections/RelativeArray.swift

@@ -260,7 +260,6 @@ extension RelativeArray {
 		_ range: Range<Index>,
 		with newElements: Elements
 	) where WeightedValue == Elements.Element, Elements : Sequence {
-		let upperRecord = storage[range.upperBound]
 		let previousWeight = findDependency(for: range.lowerBound)
 
 		// create the new records and insert them
@@ -276,8 +275,13 @@ extension RelativeArray {
 
 		storage.replaceSubrange(range, with: newRecords)
 
+		if range.upperBound >= storage.endIndex {
+			return
+		}
+
 		// and now, we have to adjust everything past the insertion
-		let delta = configuration.subtract(upperRecord.dependency, dependency)
+		let upperDependency = storage[range.upperBound].dependency
+		let delta = configuration.subtract(upperDependency, dependency)
 
 		applyDelta(delta, after: range.upperBound)
 	}

Tests/RelativeCollectionsTests/RelativeArrayTests.swift

@@ -183,4 +183,21 @@ extension RelativeArrayTests {
 
 		XCTAssertEqual(array.map { $0.value }, expected)
 	}
+
+	func testRangeReplacementEntireArray() throws {
+		var array = TestArray()
+
+		for length in [1, 2, 3, 4] {
+			array.append(.init(weight: length))
+		}
+
+		array.replaceSubrange(0..<4, with: [
+			TestArray.WeightedValue(weight: 8),
+			TestArray.WeightedValue(weight: 9)
+		])
+
+		let expected = [8, 9]
+
+		XCTAssertEqual(array.map { $0.value }, expected)
+	}
 }