user32: Fix maxPosition of thick child windows.

dlls/user32/tests/win.c

@@ -5321,10 +5321,9 @@ static LRESULT WINAPI test_thick_child_size_winproc(HWND hwnd, UINT msg, WPARAM
             expectedPosY = rect.top;
             actualPosX = minmax->ptMaxPosition.x;
             actualPosY = minmax->ptMaxPosition.y;
-            todo_wine
-                ok(actualPosX == expectedPosX && actualPosY == expectedPosY,
-                    "expected maxPosition (%d/%d), actual maxPosition (%d/%d) for %s\n",
-                    expectedPosX, expectedPosY, actualPosX, actualPosY, test_thick_child_name);
+            ok(actualPosX == expectedPosX && actualPosY == expectedPosY,
+                "expected maxPosition (%d/%d), actual maxPosition (%d/%d) for %s\n",
+                expectedPosX, expectedPosY, actualPosX, actualPosY, test_thick_child_name);
 
             break;
         }

dlls/user32/winpos.c

@@ -682,8 +682,8 @@ void WINPOS_GetMinMaxInfo( HWND hwnd, POINT *maxSize, POINT *maxPos,
         MinMax.ptMinTrackSize.y = GetSystemMetrics(SM_CYMINTRACK);
         MinMax.ptMaxTrackSize.x = GetSystemMetrics(SM_CXMAXTRACK);
         MinMax.ptMaxTrackSize.y = GetSystemMetrics(SM_CYMAXTRACK);
-
-        xinc = yinc = 0;
+        xinc = -rc.left;
+        yinc = -rc.top;
     }
     else
     {