Fix segfault from null GetFunction() in DartDumper for Dart 3.10

[vichhka-git]

Summary

• Fix SIGSEGV crash during Object Pool dump when processing Dart 3.10.7 snapshots
• GetFunction() returns nullptr when an UnlinkedCall target address isn't found in the functions/stubs maps, but 3 call sites dereference the result without null checks

Problem

When running blutter against a Dart 3.10.7 libapp.so, the binary crashes with a segmentation fault (signal 11) during DumpObjectPool(). The crash occurs in getPoolObjectDescription() when handling UnlinkedCall entries whose kImmediate target address doesn't resolve to any known function.

Related to issue #182 — commit a4d2100 added kTaggedObject handling but missed null guards on the kImmediate path.

Changes (all in blutter/src/DartDumper.cpp)

Location	Fix
getPoolObjectDescription() ~L812	Added null check on GetFunction() return; fallback to [unknown] label
DumpStructHeaderFile() ~L194	Added null check; also fixed pre-existing extra arg in std::format()
ObjectToString() ~L491	Split into null check + AsFunction() call; fallback to Function(addr)

Testing

• Verified fix against a Dart 3.10.7 Android arm64 libapp.so that previously crashed
• Full run completes successfully: Object Pool dump, code analysis, assembly generation, Frida script output all produced without error