Ensure IsConvertible() isn't checked for IsList() or getTopicReference()

Previously, the `IsConvertible()` check was bypassed if `mapAssociationsOnly` was set. That makes sense, because there's no need to call `GetScalarValue()` in that case. Except that also necessitated that each of the subsequent conditions be checked, which collectively are more expensive than the check to `IsConvertible()`. As such, since scalar values are the most common type of property we're working with, it's cheaper to put this upfront and then check `mapAssociationsOnly` within it instead.

Author: JeremyCaney

OnTopic/Mapping/TopicMappingService.cs

@@ -540,8 +540,10 @@ await MapAsync(
           value = await GetTopicReferenceAsync(source.Parent, targetType, configuration, cache).ConfigureAwait(false);
         }
       }
-      else if (!mapAssociationsOnly && AttributeValueConverter.IsConvertible(targetType)) {
-        value = GetScalarValue(source, configuration);
+      else if (AttributeValueConverter.IsConvertible(targetType)) {
+        if (!mapAssociationsOnly) {
+          value = GetScalarValue(source, configuration);
+        }
       }
       else if (IsList(targetType)) {
         return null;