Fix schema initialization paths (#3825)

* Fix schema initialization paths

The initialized channel was only closed if the schema's cacheStore did not contain the embeddedCacheKey and there were no errors parsing relations.  If the key existed or an error occurred, it would not be closed. This could leave other goroutines waiting for synchronization that will never occur.

Additionally, the other code paths that wait for initialization to complete did not return the possible error.

* Unnest common schema initialization

This makes the common code path less deeply nested and the flow control easier to follow.

schema/schema.go

@@ -92,7 +92,7 @@ func Parse(dest interface{}, cacheStore *sync.Map, namer Namer) (*Schema, error)
 	if v, ok := cacheStore.Load(modelType); ok {
 		s := v.(*Schema)
 		<-s.initialized
-		return s, nil
+		return s, s.err
 	}
 
 	modelValue := reflect.New(modelType)
@@ -223,7 +223,13 @@ func Parse(dest interface{}, cacheStore *sync.Map, namer Namer) (*Schema, error)
 		}
 	}
 
-	if s, loaded := cacheStore.LoadOrStore(modelType, schema); !loaded {
+	if v, loaded := cacheStore.LoadOrStore(modelType, schema); loaded {
+		s := v.(*Schema)
+		<-s.initialized
+		return s, s.err
+	}
+
+	defer close(schema.initialized)
 	if _, embedded := schema.cacheStore.Load(embeddedCacheKey); !embedded {
 		for _, field := range schema.Fields {
 			if field.DataType == "" && (field.Creatable || field.Updatable || field.Readable) {
@@ -249,11 +255,6 @@ func Parse(dest interface{}, cacheStore *sync.Map, namer Namer) (*Schema, error)
 				field.Schema.DeleteClauses = append(field.Schema.DeleteClauses, fc.DeleteClauses(field)...)
 			}
 		}
-			close(schema.initialized)
-		}
-	} else {
-		<-s.(*Schema).initialized
-		return s.(*Schema), nil
 	}
 
 	return schema, schema.err