Fix NaN handling in responseAdSlotCount

The function didn't validate that params.step and params.firstAdAfterNodes are
finite numbers. If they were NaN or Infinity, Math.max(1, NaN) would return NaN.

Added Number.isFinite() checks to default to safe values for invalid numbers.

Author: pavankumar-vh

common/src/util/response-ad-positions.ts

@@ -18,11 +18,10 @@ export function responseAdSlotCount(params: {
   step?: number
   firstAdAfterNodes?: number
 }): number {
-  const step = Math.max(1, params.step ?? RESPONSE_AD_NODE_STEP)
-  const firstAdAfterNodes = Math.max(
-    1,
-    params.firstAdAfterNodes ?? RESPONSE_AD_FIRST_NODE_COUNT,
-  )
+  const safeStep = params.step !== undefined && Number.isFinite(params.step) ? params.step : RESPONSE_AD_NODE_STEP
+  const safeFirstAdAfterNodes = params.firstAdAfterNodes !== undefined && Number.isFinite(params.firstAdAfterNodes) ? params.firstAdAfterNodes : RESPONSE_AD_FIRST_NODE_COUNT
+  const step = Math.max(1, safeStep)
+  const firstAdAfterNodes = Math.max(1, safeFirstAdAfterNodes)
   return Math.max(
     0,
     Math.floor((params.nodeCount - firstAdAfterNodes - 1) / step) + 1,