Add UtilityClass::Int()

This is simply a wrapper function around SDL_atoi(), because SDL_atoi()
could call libc atoi(), and whether or not invalid input passed into the
libc atoi() is undefined behavior depends on the given libc. So it's
safer to just add a wrapper function that checks that the string given
isn't bogus.

desktop_version/src/UtilityClass.cpp

@@ -99,6 +99,16 @@ std::string UtilityClass::String( int _v )
 	return(os.str());
 }
 
+int UtilityClass::Int(const char* str)
+{
+	if (!is_number(str))
+	{
+		return 0;
+	}
+
+	return SDL_atoi(str);
+}
+
 std::string UtilityClass::GCString(std::vector<SDL_GameControllerButton> buttons)
 {
 	std::string retval = "";

desktop_version/src/UtilityClass.h

@@ -37,6 +37,8 @@ public:
 
     static std::string String(int _v);
 
+    static int Int(const char* str);
+
     static std::string GCString(std::vector<SDL_GameControllerButton> buttons);
 
     std::string twodigits(int t);