[mlir][emitc] `-wrap-emitc-func-in-class` crashes on `emitc.func` declaration without a body

### Description

`mlir-opt` crashes with an assertion failure when running the `--wrap-emitc-func-in-class` pass on an `emitc.func` declaration without a body.
The crash occurs in `WrapFuncInClass::matchAndRewrite` while processing a private emitc.func.

### Tested commit

[3b8ee89](https://github.com/llvm/llvm-project/commit/3b8ee89006f5a228fce75528f8dd80b4229abcc1)

### Test case

```mlir
module {
emitc.func private @foo()
}
```

### Steps to reproduce

```
mlir-opt test.mlir --wrap-emitc-func-in-class
```

### stack trace

```
mlir-opt: /home/workdir/llvm-project-latest/llvm/include/llvm/ADT/ilist_iterator.h:168: reference llvm::ilist_iterator, false, false>::operator*() const [OptionsT = llvm::ilist_detail::node_options, IsReverse = false, IsConst = false]: Assertion `!NodePtr->isKnownSentinel()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
Stack dump:
0. Program arguments: ./mlir-opt test.mlir --wrap-emitc-func-in-class
#0 0x000055a5b9bdfd0b llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (./mlir-opt+0x1fc2d0b)
#1 0x000055a5b9bdcb11 llvm::sys::RunSignalHandlers() (./mlir-opt+0x1fbfb11)
#2 0x000055a5b9be0a3b SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0x00007ffac5a55520 (/usr/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x00007ffac5aa99fc pthread_kill (/usr/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x00007ffac5a55476 gsignal (/usr/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x00007ffac5a3b7f3 abort (/usr/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x00007ffac5a3b71b (/usr/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x00007ffac5a4ce96 (/usr/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x000055a5bb79a41c WrapFuncInClass::matchAndRewrite(mlir::emitc::FuncOp, mlir::PatternRewriter&) const (./mlir-opt+0x3b7d41c)
#10 0x000055a5c1d846c8 void llvm::function_ref::callback_fn, llvm::function_ref, llvm::function_ref)::$_0>(long) PatternApplicator.cpp:0:0
#11 0x000055a5c1d80e2a mlir::PatternApplicator::matchAndRewrite(mlir::Operation*, mlir::PatternRewriter&, llvm::function_ref, llvm::function_ref, llvm::function_ref) (./mlir-opt+0xa163e2a)
#12 0x000055a5c1d7c306 void llvm::function_ref::callback_fn(long) WalkPatternRewriteDriver.cpp:0:0
#13 0x000055a5c1d7b5c9 mlir::walkAndApplyPatterns(mlir::Operation*, mlir::FrozenRewritePatternSet const&, mlir::RewriterBase::Listener*) (./mlir-opt+0xa15e5c9)
#14 0x000055a5bb796f2e mlir::emitc::(anonymous namespace)::WrapFuncInClassPass::runOnOperation() WrapFuncInClass.cpp:0:0
#15 0x000055a5c1ddf3ee mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) (./mlir-opt+0xa1c23ee)
#16 0x000055a5c1de0364 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) (./mlir-opt+0xa1c3364)
#17 0x000055a5c1de70fa mlir::PassManager::runPasses(mlir::Operation*, mlir::AnalysisManager) (./mlir-opt+0xa1ca0fa)
#18 0x000055a5c1de6a5d mlir::PassManager::run(mlir::Operation*) (./mlir-opt+0xa1c9a5d)
#19 0x000055a5b9c8b58f performActions(llvm::raw_ostream&, std::shared_ptr const&, mlir::MLIRContext*, mlir::MlirOptMainConfig const&) MlirOptMain.cpp:0:0
#20 0x000055a5b9c8a761 llvm::LogicalResult llvm::function_ref>, llvm::MemoryBufferRef const&, llvm::raw_ostream&)>::callback_fn>, mlir::DialectRegistry&, mlir::MlirOptMainConfig const&)::$_0>(long, std::unique_ptr>, llvm::MemoryBufferRef const&, llvm::raw_ostream&) MlirOptMain.cpp:0:0
#21 0x000055a5c2139ec6 mlir::splitAndProcessBuffer(std::unique_ptr>, llvm::function_ref>, llvm::MemoryBufferRef const&, llvm::raw_ostream&)>, llvm::raw_ostream&, llvm::StringRef, llvm::StringRef) (./mlir-opt+0xa51cec6)
#22 0x000055a5b9c80ba6 mlir::MlirOptMain(llvm::raw_ostream&, std::unique_ptr>, mlir::DialectRegistry&, mlir::MlirOptMainConfig const&) (./mlir-opt+0x2063ba6)
#23 0x000055a5b9c80f7a mlir::MlirOptMain(int, char**, llvm::StringRef, llvm::StringRef, mlir::DialectRegistry&) (./mlir-opt+0x2063f7a)
#24 0x000055a5b9c811eb mlir::MlirOptMain(int, char**, llvm::StringRef, mlir::DialectRegistry&) (./mlir-opt+0x20641eb)
#25 0x000055a5b9bc57cd main (./mlir-opt+0x1fa87cd)
#26 0x00007ffac5a3cd90 (/usr/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#27 0x00007ffac5a3ce40 __libc_start_main (/usr/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#28 0x000055a5b9bc5325 _start (./mlir-opt+0x1fa8325)
Aborted (core dumped)
```

Inspect WrapFuncInClass::matchAndRewrite in WrapFuncInClass.cpp, focusing on how an emitc.func declaration without a body is handled. Run mlir-opt with the provided module and --wrap-emitc-func-in-class to reproduce the assertion. Done means the declaration no longer crashes the pass and the reproducer completes successfully.

Written by the indexing model from the issue text.