util: make sure error causes of any type may be inspected

An error cause may be of any type. Handle all of them, no matter
if they are an error or not.

Fixes: nodejs#41096

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>

lib/internal/util/inspect.js

@@ -1198,7 +1198,7 @@ function getStackFrames(ctx, err, stack) {
   const frames = stack.split('\n');
 
   // Remove stack frames identical to frames in cause.
-  if (err.cause) {
+  if (err.cause && isError(err.cause)) {
     const causeStack = getStackString(err.cause);
     const causeStackStart = causeStack.indexOf('\n    at');
     if (causeStackStart !== -1) {

test/message/util-inspect-error-cause.js

@@ -13,6 +13,18 @@ const cause2 = new FoobarError('Individual message', { cause: cause1 });
 cause2.extraProperties = 'Yes!';
 const cause3 = new Error('Stack causes', { cause: cause2 });
 
+const cause4 = new Error('No error cause', { cause: 42 });
+const cause5 = new Error('Object cause', {
+  cause: {
+    message: 'Unique',
+    name: 'Error',
+    stack: 'Error: Unique\n    at Module._compile (node:internal/modules/cjs/loader:827:30)'
+  }
+});
+
+console.log(cause4);
+console.log(cause5);
+
 process.nextTick(() => {
   const error = new RangeError('New Stack Frames', { cause: cause2 });
   const error2 = new RangeError('New Stack Frames', { cause: cause3 });

test/message/util-inspect-error-cause.out

@@ -1,3 +1,28 @@
+Error: No error cause
+    at *
+    at *
+    at *
+    at *
+    at *
+    at *
+    at * {
+  [cause]: 42
+}
+Error: Object cause
+    at *
+    at *
+    at *
+    at *
+    at *
+    at *
+    at * {
+  [cause]: {
+    message: 'Unique',
+    name: 'Error',
+    stack: 'Error: Unique\n' +
+      '    at Module._compile (node:internal/modules/cjs/loader:827:30)'
+  }
+}
 RangeError: New Stack Frames
     at *
 *[90m    at *[39m {