Fix an invalid pointer comparison triggered by renaming a table column when

there are views with explicit column names in the schema.

FossilOrigin-Name: 572de7e4e33562c72cd90790b267ba389370f21ddcaebc4db609fd76ae9b7ada

src/alter.c

@@ -723,6 +723,24 @@ void sqlite3RenameExprUnmap(Parse *pParse, Expr *pExpr){
   sqlite3WalkExpr(&sWalker, pExpr);
 }
 
+/*
+** Remove all nodes that are part of expression-list pEList from the 
+** rename list.
+*/
+void sqlite3RenameExprlistUnmap(Parse *pParse, ExprList *pEList){
+  if( pEList ){
+    int i;
+    Walker sWalker;
+    memset(&sWalker, 0, sizeof(Walker));
+    sWalker.pParse = pParse;
+    sWalker.xExprCallback = renameUnmapExprCb;
+    sqlite3WalkExprList(&sWalker, pEList);
+    for(i=0; i<pEList->nExpr; i++){
+      sqlite3RenameTokenRemap(pParse, 0, (void*)pEList->a[i].zName);
+    }
+  }
+}
+
 /*
 ** Free the list of RenameToken objects given in the second argument
 */