module: don't read a phantom name on the last mapping segment

lib/internal/source_map/source_map.js

@@ -300,7 +300,8 @@ class SourceMap {
       sourceColumnNumber += decodeVLQ(stringCharIterator);
 
       let name;
-      if (!isSeparator(stringCharIterator.peek())) {
+      if (stringCharIterator.hasNext() &&
+          !isSeparator(stringCharIterator.peek())) {
         nameIndex += decodeVLQ(stringCharIterator);
         name = map.names?.[nameIndex];
       }

test/parallel/test-source-map-trailing-name.js

@@ -0,0 +1,34 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const { SourceMap } = require('node:module');
+
+// Refs: https://github.com/nodejs/node/issues/63795
+
+// A mapping whose final segment has 4 fields (no name index) must not
+// inherit the previous segment's name.
+{
+  const sm = new SourceMap({
+    version: 3,
+    sources: ['a.js'],
+    names: ['foo'],
+    mappings: 'AAAAA,CAAC',
+  });
+
+  assert.strictEqual(sm.findEntry(0, 0).name, 'foo');
+  assert.strictEqual(sm.findEntry(0, 1).name, undefined);
+}
+
+// A mapping whose final segment legitimately carries a name index must still
+// resolve it: the end-of-string guard must not suppress a real trailing name.
+{
+  const sm = new SourceMap({
+    version: 3,
+    sources: ['a.js'],
+    names: ['foo'],
+    mappings: 'AAAA,CAAAA',
+  });
+
+  assert.strictEqual(sm.findEntry(0, 0).name, undefined);
+  assert.strictEqual(sm.findEntry(0, 1).name, 'foo');
+}