[Sol->Yul] ICE because IR generator cannot parse location specification

Repro:

1. Create a file called `p @src 0:` as follows

```
$ cat < p\ \@src\ 0:
contract C { }
EOF
```

2. Compile said file via IR

```
$ solc p\ @src\ 0\: --ir
```

throws

https://github.com/ethereum/solidity/blob/84cdcec2cfb1fe9d4a9171d3ed0ffefd6107ee42/libsolidity/codegen/ir/IRGenerator.cpp#L112

Reproduce the ICE with the documented filename and `solc p\ @src\ 0\: --ir` command. Then inspect `libsolidity/codegen/ir/IRGenerator.cpp` around line 112 to trace how the location specification is parsed. Done means the same input compiles through IR without the internal compiler error.

Written by the indexing model from the issue text.