make it even saferer

src/libui_sdl/main.cpp

@@ -1575,6 +1575,8 @@ int main(int argc, char** argv)
             if (argv[0][len] == '\\') break;
             len--;
         }
+        if (len > 0)
+        {
             EmuDirectory = new char[len];
             strncpy(EmuDirectory, argv[0], len);
             EmuDirectory[len] = '\0';
@@ -1584,6 +1586,12 @@ int main(int argc, char** argv)
             EmuDirectory = new char[2];
             strcpy(EmuDirectory, ".");
         }
+    }
+    else
+    {
+        EmuDirectory = new char[2];
+        strcpy(EmuDirectory, ".");
+    }
 
     // http://stackoverflow.com/questions/14543333/joystick-wont-work-using-sdl
     SDL_SetHint(SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS, "1");