fix(serialization): fix parse crash on null pointer dereference in resize (#107)

Fixes issue similar to #78 (perhaps same) where a sender doesn't set a text field in the source proto can cause a unexpected validation error on the receiver when parsing the proto message.

What appears to happen is a null source pointer is dereferenced and the data is assigned to the destination pointer in the resize function.

Author: cmbartschat

packages/capnp-ts/src/serialization/pointers/struct.ts

@@ -238,6 +238,10 @@ export function resize(dstSize: ObjectSize, s: Struct): void {
       srcContent.segment,
       srcContent.byteOffset + srcSize.dataByteLength + i * 8
     );
+    if (isNull(srcPtr)) {
+      // If source pointer is null, leave the destination pointer as default null.
+      continue
+    }
     const srcPtrTarget = followFars(srcPtr);
     const srcPtrContent = getContent(srcPtr);
     const dstPtr = new Pointer(