[NFC] Using precondition instead of assert in calls that do not allow negative values

Author: LucianoPAlmeida

Sources/Algorithms/Combinations.swift

@@ -286,7 +286,7 @@ extension Collection {
   /// accesses the `count` of the base collection.
   @inlinable
   public func combinations(ofCount k: Int) -> Combinations<Self> {
-    assert(k >= 0, "Can't have combinations with a negative number of elements.")
+    precondition(k >= 0, "Can't have combinations with a negative number of elements.")
     return Combinations(self, k: k)
   }
 }

Sources/Algorithms/Permutations.swift

@@ -242,7 +242,7 @@ extension Collection {
   ///
   /// - Complexity: O(1)
   public func permutations(ofCount k: Int? = nil) -> Permutations<Self> {
-    assert(
+    precondition(
       k ?? 0 >= 0,
       "Can't have permutations with a negative number of elements.")
     return Permutations(self, k: k)