fix: only set send reason to span limit if it's configured (#1290)

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## Which problem is this PR solving?

We should not set send reason to span limit if users didn't specify the
span limit config

## Short description of the changes

- only set send reason to span limit if span limit config is non-zero

collect/collect.go

@@ -456,7 +456,7 @@ func (i *InMemCollector) sendExpiredTracesInCache(now time.Time) {
 		if t.RootSpan != nil {
 			i.send(t, TraceSendGotRoot)
 		} else {
-			if t.SpanCount() > spanLimit {
+			if spanLimit > 0 && t.SpanCount() > spanLimit {
 				i.send(t, TraceSendSpanLimit)
 			} else {
 				i.send(t, TraceSendExpired)

collect/collect_test.go

@@ -1773,7 +1773,6 @@ func TestDrainTracesOnShutdown(t *testing.T) {
 
 	sentTraceChan := make(chan sentRecord, 1)
 	forwardTraceChan := make(chan *types.Span, 1)
-	expiredTraceChan := make(chan *types.Span, 1)
 
 	// test 1
 	// the trace in cache already has decision made
@@ -1793,7 +1792,6 @@ func TestDrainTracesOnShutdown(t *testing.T) {
 	coll.distributeSpansOnShutdown(sentTraceChan, forwardTraceChan, span1)
 	require.Len(t, sentTraceChan, 1)
 	require.Len(t, forwardTraceChan, 0)
-	require.Len(t, expiredTraceChan, 0)
 
 	ctx1, cancel1 := context.WithCancel(context.Background())
 	go coll.sendSpansOnShutdown(ctx1, sentTraceChan, forwardTraceChan)
@@ -1822,7 +1820,6 @@ func TestDrainTracesOnShutdown(t *testing.T) {
 	coll.distributeSpansOnShutdown(sentTraceChan, forwardTraceChan, span2)
 	require.Len(t, sentTraceChan, 0)
 	require.Len(t, forwardTraceChan, 1)
-	require.Len(t, expiredTraceChan, 0)
 
 	ctx2, cancel2 := context.WithCancel(context.Background())
 	go coll.sendSpansOnShutdown(ctx2, sentTraceChan, forwardTraceChan)