Add integer check for alphabet size

Fixes "Generate De Bruijn Sequence - RangeError in blob:null/6895a5cc-cf19-4023-b300-36e358dad354 on line 2.<br><br>Message: invalid array length"

src/core/operations/GenerateDeBruijnSequence.mjs

@@ -50,6 +50,10 @@ class GenerateDeBruijnSequence extends Operation {
             throw new OperationError("Invalid alphabet size, required to be between 2 and 9 (inclusive).");
         }
 
+        if (!Number.isInteger(k)) {
+            throw new OperationError("Invalid alphabet size, required to be integer.");
+        }
+
         if (n < 2) {
             throw new OperationError("Invalid key length, required to be at least 2.");
         }