Fix a code-generator issue associated with very unusual use of window

Fix a code-generator issue associated with very unusual use of window
functions.  Both the expr.c or the window.c changes will each
independently fix the problem.  They are both included in this patch for
defense in depth.  [forum:/forumpost/0d48347967|Forum post 0d48347967].

FossilOrigin-Name: 1ba22631a7831e3562eda0eb6a5edf7f009c85c7ab4451d9eacd13ef0fb6036a