fix skiaserve crash

tools/skiaserve/skiaserve.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrCaps.h"
 #include "GrContextFactory.h"
 #include "SkCanvas.h"
@@ skipping 192 matching lines @@
         return 0 == strcmp(method, MHD_HTTP_METHOD_GET) &&
                0 == strncmp(url, kBasePath, strlen(kBasePath));
     }
 
     int handle(Request* request, MHD_Connection* connection,
                const char* upload_data, size_t* upload_data_size) override {
         if (request->fPNG.get()) {
             SkData* data = request->fPNG.get();
             return SendData(connection, data, "image/png");
         }
+
         return MHD_NO;
     }
 };
 
 class PostHandler : public UrlHandler {
 public:
     bool canHandle(const char* method, const char* url) override {
         return 0 == strcmp(method, MHD_HTTP_METHOD_POST) &&
                0 == strcmp(url, "/new");
     }
@@ skipping 27 matching lines @@
         MHD_destroy_post_processor(uc->fPostProcessor);
         uc->fPostProcessor = nullptr;
 
         // TODO response
         SkString error;
         if (!setupAndDrawToCanvas(request, &error)) {
             // TODO send error
             return MHD_YES;
         }
 
+        // clear upload context
+        delete request->fUploadContext;
+        request->fUploadContext = nullptr;
+
         return SendTemplate(connection, true, "/");
     }
 };
 
 class RootHandler : public UrlHandler {
 public:
     bool canHandle(const char* method, const char* url) override {
         return 0 == strcmp(method, MHD_HTTP_METHOD_GET) &&
                0 == strcmp(url, "/");
     }
@@ skipping 65 matching lines @@
     MHD_stop_daemon(daemon);
     return 0;
 }
 
 #if !defined SK_BUILD_FOR_IOS
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return skiaserve_main();
 }
 #endif