fix: undefined place in vFile message causes TypeError (#521)

Many remark-lint errors do not set a place variable in the vFile
message. This code should accept undefined for this field.

fixes #520

Co-authored-by: JounQin <admin@1stg.me>

.changeset/new-brooms-visit.md

@@ -0,0 +1,10 @@
+---
+"eslint-plugin-mdx": patch
+---
+
+fix: `undefined` `place` in vFile message causes TypeError
+
+Many `remark-lint` errors do not set a place variable in the vFile
+message. This code should accept `undefined` for this field.
+
+fixes #520

packages/eslint-plugin-mdx/src/rules/remark.ts

@@ -100,7 +100,7 @@ export const remark: Rule.RuleModule = {
             // related to https://github.com/eslint/eslint/issues/14198
             message: JSON.stringify(message),
             loc:
-              /* istanbul ignore next */ 'start' in place
+              /* istanbul ignore next */ place && 'start' in place
                 ? {
                     ...point,
                     start: { ...place.start, column: place.start.column - 1 },