main: Resolve error string not displaying

During the transition to make the error dialog translatable, I
accidentally got rid of the conversion to ResultStatus, which prevented
operator<< from being invoked during formatting.

This adds a function to directly retrieve the result status string
instead so that it displays again.

src/core/loader/loader.h

@@ -135,6 +135,7 @@ enum class ResultStatus : u16 {
     ErrorINITooManyKIPs,
 };
 
+std::string GetResultStatusString(ResultStatus status);
 std::ostream& operator<<(std::ostream& os, ResultStatus status);
 
 /// Interface for loading an application