Fix NPE in TextKeyReader if the input is invalid

Signed-off-by: Graham <gpe@openrs2.org>

archive/src/main/kotlin/org/openrs2/archive/key/TextKeyReader.kt

@@ -7,10 +7,10 @@ public object TextKeyReader : KeyReader {
     override fun read(input: InputStream): Sequence<XteaKey> {
         val reader = input.bufferedReader()
 
-        val k0 = reader.readLine().toIntOrNull() ?: return emptySequence()
-        val k1 = reader.readLine().toIntOrNull() ?: return emptySequence()
-        val k2 = reader.readLine().toIntOrNull() ?: return emptySequence()
-        val k3 = reader.readLine().toIntOrNull() ?: return emptySequence()
+        val k0 = reader.readLine()?.toIntOrNull() ?: return emptySequence()
+        val k1 = reader.readLine()?.toIntOrNull() ?: return emptySequence()
+        val k2 = reader.readLine()?.toIntOrNull() ?: return emptySequence()
+        val k3 = reader.readLine()?.toIntOrNull() ?: return emptySequence()
 
         return sequenceOf(XteaKey(k0, k1, k2, k3))
     }