Throw an error if zcash.conf is missing

An empty zcash.conf is sufficient to bypass this error.

src/util.cpp

@@ -534,7 +534,7 @@ void ReadConfigFile(map<string, string>& mapSettingsRet,
 {
     boost::filesystem::ifstream streamConfig(GetConfigFile());
     if (!streamConfig.good())
-        return; // No zcash.conf file is OK
+        throw missing_zcash_conf();
 
     set<string> setOptions;
     setOptions.insert("*");

src/util.h

@@ -127,6 +127,10 @@ boost::filesystem::path GetConfigFile();
 boost::filesystem::path GetPidFile();
 void CreatePidFile(const boost::filesystem::path &path, pid_t pid);
 #endif
+class missing_zcash_conf : public std::runtime_error {
+public:
+    missing_zcash_conf() : std::runtime_error("Missing zcash.conf") { }
+};
 void ReadConfigFile(std::map<std::string, std::string>& mapSettingsRet, std::map<std::string, std::vector<std::string> >& mapMultiSettingsRet);
 #ifdef WIN32
 boost::filesystem::path GetSpecialFolderPath(int nFolder, bool fCreate = true);