[TypeChecker] ICE in spurious dragon due to unset return parameter decoding type in recursive library function call with a return function type

```
library L {
function f() returns (function() r) {
L.f();
}
}
```

throws

https://github.com/ethereum/solidity/blob/defc74c8a248585b9fe1ddc8a10d10f11c92c052/libsolidity/ast/Types.cpp#L2877

Repro:

```
$ solc --evm-version spuriousDragon test.sol
```

Reproduce the ICE with `solc --evm-version spuriousDragon test.sol` using the recursive library example. Start at the referenced `libsolidity/ast/Types.cpp` location around line 2877 and trace the return-function type decoding path. Done means the example no longer triggers an internal compiler error, with regression coverage for the case.

Written by the indexing model from the issue text.