process: fix two overflow cases in SourceMap VLQ decoding

lib/internal/source_map/source_map.js

@@ -303,8 +303,20 @@ function decodeVLQ(stringCharIterator) {
 
   // Fix the sign.
   const negative = result & 1;
-  result >>= 1;
-  return negative ? -result : result;
+  // Use unsigned right shift, so that the 32nd bit is properly shifted to the
+  // 31st, and the 32nd becomes unset.
+  result >>>= 1;
+  if (!negative) {
+    return result;
+  }
+
+  // We need to OR 0x80000000 here to ensure the 32nd bit (the sign bit in a
+  // 32bit int) is always set for negative numbers. If `result` were 1,
+  // (meaning `negate` is true and all other bits were zeros), `result` would
+  // now be 0. But -0 doesn't flip the 32nd bit as intended. All other numbers
+  // will successfully set the 32nd bit without issue, so doing this is a noop
+  // for them.
+  return -result | 0x80000000;
 }
 
 /**