fix GuiHandler crashes

rts/Game/UI/GuiHandler.cpp

@@ -2969,8 +2969,8 @@ void CGuiHandler::DrawButtons() // Only called by Draw
 	}
 
 	const int mouseIcon   = IconAtPos(mouse->lastx, mouse->lasty);
-	const int buttonStart = std::min(iconsCount, activePage * iconsPerPage);
-	const int buttonEnd   = std::min(iconsCount, buttonStart + iconsPerPage);
+	const int buttonStart = Clamp( activePage * iconsPerPage, 0, iconsCount); // activePage can be -1
+	const int buttonEnd   = Clamp(buttonStart + iconsPerPage, 0, iconsCount);
 
 	for (int ii = buttonStart; ii < buttonEnd; ii++) {
 		const IconInfo& icon = icons.at(ii);