assert: handle undefined filename in getErrMessage

When generating an assertion error message,
`filename` might be undefined,
e.g. if `assert` is called in `eval`.

Handle this case gracefully instead of failing with
`Cannot read property 'endsWith' of undefined`.

Fixes: #20847

lib/assert.js

@@ -154,6 +154,10 @@ function getBuffer(fd, assertLine) {
 
 function getErrMessage(call) {
   const filename = call.getFileName();
+  if (!filename) {
+    return;
+  }
+
   const line = call.getLineNumber() - 1;
   const column = call.getColumnNumber() - 1;
   const identifier = `${filename}${line}${column}`;

test/parallel/test-assert.js

@@ -742,6 +742,16 @@ common.expectsError(
   }
 );
 
+// works in eval
+common.expectsError(
+  () => new Function('assert', 'assert(1 === 2);')(assert),
+  {
+    code: 'ERR_ASSERTION',
+    type: assert.AssertionError,
+    message: 'false == true'
+  }
+);
+
 // Do not try to check Node.js modules.
 {
   const e = new EventEmitter();