[Flang][OpenMP] Incorrect execution results when continuation lines of OpenMP (free source form conditional compilation sentinel) and Fortran `free source form` are mixed

## Summary

This is a similar issue to #89559, which reported a compilation error. The compilation now succeeds, but the execution result is incorrect.

### Reproducer

* ompc_066_.f90

```fortran
program main
!$ i = 0
i = 1&
!$ +10 &
!$+100&
!$&+ 1000&
&+ 10000&
!$& +100000&
& +1000000

if(i .eq. 1111111) then
print *, 'OK'
else
print *, 'NG'
endif
end program main
```

* commands

```console
$ flang --version
flang version 23.0.0git (https://github.com/llvm/llvm-project.git 3e20d3d3964a3a6ac5f882842c7716e2682d622f)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /path/to/llvm/build/bin
Build config: +assertions
$ flang -fopenmp ompc_066_.f90 && ./a.out
NG
```

## Non-problematic Conditions

The issue does not occur under the following conditions:
* Adding a white space or an ampersand after the conditional compilation sentinel:
```diff
@@ -2,7 +2,7 @@
!$ i = 0
i = 1&
!$ +10 &
-!$+100&
+!$ +100&
!$&+ 1000&
&+ 10000&
!$& +100000&
```

## Other Compilers

* GFortran
```console
$ gfortran --version
GNU Fortran (GCC) 15.2.0
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gfortran -fopenmp ompc_066_.f90 && ./a.out
OK
```

* Intel Fortran
```console
$ ifx --version
ifx (IFX) 2025.3.2 20260112
Copyright (C) 1985-2026 Intel Corporation. All rights reserved.

$ ifx -qopenmp ompc_066_.f90 && ./a.out
OK
```

The reproducer is ompc_066_.f90; first run flang -fopenmp ompc_066_.f90 && ./a.out and confirm it prints NG. Trace Flang's handling of mixed free-form continuation lines and OpenMP conditional-compilation sentinels, then verify the program prints OK under the same command.

Written by the indexing model from the issue text.