fix: force met.Numerator to be equals with met.Denominator when met.Numerator <= 0

Author: Starrah

generator/chu/UgcGenerator.cs

@@ -90,13 +90,15 @@ void Dfs(ChuNote n)
     private void FillUgcBeats(List<MET> metList)
     {
         _ugcBeats = [];
-        foreach (var met in metList)
+        foreach (var origMet in metList)
         {
-            if (met.Numerator <= 0 || met.Denominator <= 0)
+            var met = origMet;
+            if (met.Numerator <= 0)
             {
-                alerts.Add(new Alert(Alert.LEVEL.Warning,
-                    $"UGC Generator忽略无效拍号: {met.Numerator}/{met.Denominator}", met.Time));
-                continue;
+                // See https://github.com/MuNET-OSS/MuConvert/pull/7#discussion_r4217218971 ,
+                // in official game, met.Numerator == 0 means there should be no "beat lines", which cannot be easily implemented in Umiguri.
+                // But this will cause DivideByZeroException in the `T` function, so we just force met.Numerator to be equals with met.Denominator.
+                met = met with { Numerator = met.Denominator };
             }
 
             if (_ugcBeats.Count == 0)

tests/chu/UgcTimeTests.cs

@@ -118,7 +118,6 @@ public void UgcGenerator_IgnoresZeroNumeratorMeterAndKeepsMappingLaterNotes()
 
         var (ugc, alerts) = new UgcGenerator().Generate(chart);
 
-        Assert.Single(alerts);
         Assert.Contains("@BEAT\t1\t1\t4", ugc);
         Assert.DoesNotContain("@BEAT\t9\t0\t4", ugc);
         Assert.Contains("#9'0:t01", ugc);