Corrected YAML file parsing

* Fixes #2323.
* YAML file parsing will now properly catch and display warnings when unable to read a file.
Thanks to @CairoLee!

3rdparty/yaml-cpp/src/parse.cpp

@@ -31,7 +31,7 @@ Node Load(std::istream& input) {
 
 Node LoadFile(const std::string& filename) {
   std::ifstream fin(filename.c_str());
-  if (!fin) {
+  if (fin.bad()) {
     throw BadFile();
   }
   return Load(fin);

src/common/yamlwrapper.cpp

@@ -47,6 +47,8 @@ yamlwrapper* yaml_load_file(const char* file_name) {
 		node = YAML::LoadFile(file_name);
 		if (!node.IsDefined())
 			return NULL;
+		if (node.IsNull())
+			return NULL;
 	} catch (YAML::ParserException &e) {
 		ShowError("YAML Exception Caught: %s\n", e.what());
 		return NULL;