Fixed MousePosPrev with has never been valid outside of NewFrame().

bed6ef03f always worked because it was done in NewFrame() before the assignment.

imgui.cpp

@@ -5082,6 +5082,7 @@ void ImGui::EndFrame()
     g.IO.Fonts->Locked = false;
 
     // Clear Input data for next frame
+    g.IO.MousePosPrev = g.IO.MousePos;
     g.IO.AppFocusLost = false;
     g.IO.MouseWheel = g.IO.MouseWheelH = 0.0f;
     g.IO.InputQueueCharacters.resize(0);
@@ -8670,7 +8671,6 @@ static void ImGui::UpdateMouseInputs()
     if (io.MouseDelta.x != 0.0f || io.MouseDelta.y != 0.0f)
         g.NavDisableMouseHover = false;
 
-    io.MousePosPrev = io.MousePos;
     for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++)
     {
         io.MouseClicked[i] = io.MouseDown[i] && io.MouseDownDuration[i] < 0.0f;