Backends: Win32: fixed an issue where a viewport destroyed while clicking would hog mouse tracking and temporary lead to incorrect update of HoveredWindow. (#7971)

# Conflicts:
#	backends/imgui_impl_win32.cpp
#	docs/CHANGELOG.txt

backends/imgui_impl_win32.cpp

@@ -107,7 +107,7 @@ struct ImGui_ImplWin32_Data
 {
     HWND                        hWnd;
     HWND                        MouseHwnd;
-    int                         MouseTrackedArea;   // 0: not tracked, 1: client are, 2: non-client area
+    int                         MouseTrackedArea;   // 0: not tracked, 1: client area, 2: non-client area
     int                         MouseButtonsDown;
     INT64                       Time;
     INT64                       TicksPerSecond;
@@ -629,6 +629,16 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
         }
         return 0;
     }
+    case WM_DESTROY:
+        if (bd->MouseHwnd == hwnd && bd->MouseTrackedArea != 0)
+        {
+            TRACKMOUSEEVENT tme_cancel = { sizeof(tme_cancel), TME_CANCEL, hwnd, 0 };
+            ::TrackMouseEvent(&tme_cancel);
+            bd->MouseHwnd = nullptr;
+            bd->MouseTrackedArea = 0;
+            io.AddMousePosEvent(-FLT_MAX, -FLT_MAX);
+        }
+        return 0;
     case WM_LBUTTONDOWN: case WM_LBUTTONDBLCLK:
     case WM_RBUTTONDOWN: case WM_RBUTTONDBLCLK:
     case WM_MBUTTONDOWN: case WM_MBUTTONDBLCLK: