fix: handle fetch's count in a way that matches roundtrip

Author: Blizzara

spark/src/main/scala/io/substrait/spark/logical/ToLogicalPlan.scala

@@ -215,7 +215,7 @@ class ToLogicalPlan(spark: SparkSession) extends DefaultRelVisitor[LogicalPlan]
 
   override def visit(fetch: relation.Fetch): LogicalPlan = {
     val child = fetch.getInput.accept(this)
-    val limit = fetch.getCount.getAsLong.intValue()
+    val limit = fetch.getCount.orElse(-1).intValue()
     val offset = fetch.getOffset.intValue()
     val toLiteral = (i: Int) => Literal(i, IntegerType)
     if (limit >= 0) {

spark/src/main/scala/io/substrait/spark/logical/ToSubstraitRel.scala

@@ -206,12 +206,15 @@ class ToSubstraitRel extends AbstractLogicalPlanVisitor with Logging {
   }
 
   private def fetch(child: LogicalPlan, offset: Long, limit: Long = -1): relation.Fetch = {
-    relation.Fetch
+    val builder = relation.Fetch
       .builder()
       .input(visit(child))
       .offset(offset)
-      .count(limit)
-      .build()
+    if (limit != -1) {
+      builder.count(limit)
+    }
+
+      builder.build()
   }
 
   override def visitGlobalLimit(p: GlobalLimit): relation.Rel = {