cfg: turn a handful of parameter parsing errors into fatal (#554)

For parameters that require two values (`width, height` or `x, y`), if
the string fails to parse, turn into runtime failure.

src/spice2x/overlay/windows/iidx_sub.cpp

@@ -13,7 +13,7 @@ namespace overlay::windows {
 
         if (GRAPHICS_IIDX_WSUB) {
             this->disabled_message =
-                "Close this overlay and use the second window.\n"
+                "Close this overlay and use the second window (ALT+TAB).\n"
                 "If you don't see the window, double check your DLL type and apply TDJ I/O patches as needed.";
         } else if (games::iidx::IIDX_TDJ_MONITOR_WARNING) {
             this->disabled_message = "TDJ mode subscreen overlay is not compatible with -monitor option";