Format error message.

Add regression test of issue-416.

tests/issue-416.gltf

@@ -0,0 +1 @@
+{"images":[{"uri":"%!QAAAQAAA5"}],"asset":{"version":""}}

tests/tester.cc

@@ -738,3 +738,22 @@ TEST_CASE("filesize-check", "[issue-416]") {
 
   REQUIRE(false == ret);
 }
+
+TEST_CASE("load-issue-416-model", "[issue-416]") {
+
+  tinygltf::Model model;
+  tinygltf::TinyGLTF ctx;
+  std::string err;
+  std::string warn;
+
+  bool ret = ctx.LoadASCIIFromFile(&model, &err, &warn, "issue-416.gltf");
+  if (!warn.empty()) {
+    std::cout << "WARN:" << warn << std::endl;
+  }
+  if (!err.empty()) {
+    std::cerr << "ERR:" << err << std::endl;
+  }
+
+  // external file load fails, but reading glTF itself is ok.
+  REQUIRE(true == ret);
+}

tiny_gltf.h

@@ -4177,8 +4177,8 @@ static bool ParseImage(Image *image, const int image_idx, std::string *err,
     if (!uri_cb->decode(uri, &decoded_uri, uri_cb->user_data)) {
       if (warn) {
         (*warn) += "Failed to decode 'uri' for image[" +
-                   std::to_string(image_idx) + "] name = [" + image->name +
-                   "]\n";
+                   std::to_string(image_idx) + "] name = \"" + image->name +
+                   "\"\n";
       }
 
       // Image loading failure is not critical to overall gltf loading.
@@ -4190,8 +4190,8 @@ static bool ParseImage(Image *image, const int image_idx, std::string *err,
                           /* checksize */ false, /* max file size */ max_file_size, fs)) {
       if (warn) {
         (*warn) += "Failed to load external 'uri' for image[" +
-                   std::to_string(image_idx) + "] name = [" + decoded_uri +
-                   "]\n";
+                   std::to_string(image_idx) + "] name = \"" + decoded_uri +
+                   "\"\n";
       }
       // If the image cannot be loaded, keep uri as image->uri.
       return true;
@@ -4200,8 +4200,8 @@ static bool ParseImage(Image *image, const int image_idx, std::string *err,
     if (img.empty()) {
       if (warn) {
         (*warn) += "Image data is empty for image[" +
-                   std::to_string(image_idx) + "] name = [" + image->name +
-                   "] \n";
+                   std::to_string(image_idx) + "] name = \"" + image->name +
+                   "\" \n";
       }
       return false;
     }