Viewport, Platform: Fixed a crash if the back-end set the PlatformRequestMove/PlatformRequestSize flags while viewports were disabled (it happened in the SDL back-end, and generally we want to tolerate it to make back-end implementation simpler). (#1542)

imgui.cpp

@@ -3555,6 +3555,8 @@ static void ImGui::UpdateViewports()
             continue;
         }
 
+        if ((g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
+        {
             // Apply Position and Size (from Platform Window to ImGui) if requested. 
             // We do it early in the frame instead of waiting for UpdatePlatformWindows() to avoid a frame of lag when moving/resizing using OS facilities.
             if (viewport->PlatformRequestMove)
@@ -3571,6 +3573,7 @@ static void ImGui::UpdateViewports()
 
             // Update monitor (we'll use this info to clamp windows and save windows lost in a removed monitor)
             viewport->PlatformMonitor = FindPlatformMonitorForRect(viewport->GetRect());
+        }
 
         // Update DPI scale
         float new_dpi_scale;