Improve performance of simple reflist merges

When merging reflists with ignoreConflicting set to true and
overrideMatching set to false, the individual ref components are never
examined, but the refs are still split anyway. Avoiding the split when
we never use the components brings a massive speedup: on my system, the
included benchmark goes from ~1500 us/it to ~180 us/it.

Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

deb/reflist_bench_test.go

@@ -0,0 +1,30 @@
+package deb
+
+import (
+	"fmt"
+	"sort"
+	"testing"
+)
+
+func BenchmarkReflistSimpleMerge(b *testing.B) {
+	const count = 4096
+
+	l := NewPackageRefList()
+	r := NewPackageRefList()
+
+	for i := 0; i < count; i++ {
+		if i%2 == 0 {
+			l.Refs = append(l.Refs, []byte(fmt.Sprintf("Pamd64 pkg%d %d", i, i)))
+		} else {
+			r.Refs = append(r.Refs, []byte(fmt.Sprintf("Pamd64 pkg%d %d", i, i)))
+		}
+	}
+
+	sort.Sort(l)
+	sort.Sort(r)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Merge(r, false, true)
+	}
+}