Custom expression editor: don't process invalid expression (#19533)

If the expression is not valid, i.e. there is an error message
associated with processing it, do not blindly continue with it, since it
leads to a potential rewrite of the expression (the rest of
the parser/compiler can tolerate certain brokenness).

frontend/src/metabase/query_builder/components/expressions/ExpressionEditorTextfield.jsx

@@ -255,16 +255,18 @@ export default class ExpressionEditorTextfield extends React.Component {
     this.setState({ errorMessage });
 
     // whenever our input blurs we push the updated expression to our parent if valid
-    const expression = this.compileExpression();
-    if (expression) {
-      if (!isExpression(expression)) {
-        console.warn("isExpression=false", expression);
-      }
-      this.props.onChange(expression);
-    } else if (errorMessage) {
+    if (errorMessage) {
       this.props.onError(errorMessage);
     } else {
-      this.props.onError({ message: t`Invalid expression` });
+      const expression = this.compileExpression();
+      if (expression) {
+        if (!isExpression(expression)) {
+          console.warn("isExpression=false", expression);
+        }
+        this.props.onChange(expression);
+      } else {
+        this.props.onError({ message: t`Invalid expression` });
+      }
     }
   };