Use defer to ensure cleanup is handled correctly

Author: tbkka

Sources/SwiftProtobuf/JSONEncodingVisitor.swift

@@ -298,8 +298,11 @@ internal struct JSONEncodingVisitor: Visitor {
         encoder.append(text: json)
       }
     } else if let newNameMap = (M.self as? _ProtoNameProviding.Type)?._protobuf_nameMap {
+      // Install inner object's name map
       let oldNameMap = self.nameMap
       self.nameMap = newNameMap
+      // Restore outer object's name map before returning
+      defer { self.nameMap = oldNameMap }
       for v in value {
         if comma {
           encoder.comma()
@@ -309,7 +312,6 @@ internal struct JSONEncodingVisitor: Visitor {
         try v.traverse(visitor: &self)
         encoder.endObject()
       }
-      self.nameMap = oldNameMap
     } else {
       throw JSONEncodingError.missingFieldNames
     }

Sources/SwiftProtobuf/TextFormatEncodingVisitor.swift

@@ -246,6 +246,12 @@ internal struct TextFormatEncodingVisitor: Visitor {
       self.nameMap = (M.self as? _ProtoNameProviding.Type)?._protobuf_nameMap
       self.nameResolver = [:]
       self.extensions = (value as? ExtensibleMessage)?._protobuf_extensionFieldValues
+      // Restore state before returning
+      defer {
+        self.extensions = oldExtensions
+        self.nameResolver = oldNameResolver
+        self.nameMap = oldNameMap
+      }
       // Encode submessage
       encoder.startMessageField()
       if let any = value as? Google_Protobuf_Any {
@@ -254,10 +260,6 @@ internal struct TextFormatEncodingVisitor: Visitor {
           try! value.traverse(visitor: &self)
       }
       encoder.endMessageField()
-      // Restore state
-      self.extensions = oldExtensions
-      self.nameResolver = oldNameResolver
-      self.nameMap = oldNameMap
   }
 
   // Emit the full "verbose" form of an Any.  This writes the typeURL