With rc.regex:off set, filter containing a slash produces an error

```
$ task rc.regex:off 'review / reconcile failing CArk accounts' list
Configuration override rc.regex:off
Cannot divide real numbers by strings
```

But if I trim the slash and the leading string, results are returned:

```
$ task rc.regex:off 'reconcile failing CArk accounts' list
Configuration override rc.regex:off

ID Age Project Description Urg
--- --- ---------- -------------------------------------------- ----
537 1d [pro-secr] review / reconcile failing CArk accounts 1.01

1 task
```
I run it in Msys2 environment (a Cygwin fork) on w10:

```
$ task diag

task 2.5.1
Platform:

Compiler
Version: 6.4.0
Caps: +stdc +stdc_hosted +200809 +200809 +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
Built: Jan 24 2018 22:37:20
CMake: 3.9.6
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.6.1
Build type: release

Configuration
File: /home/saukrs/.taskrc (found), 1409 bytes, mode 100644
Data: /home/saukrs/.task (found), dir, mode 40755
Locking: Enabled
GC: Enabled
Server:
Trust: strict
Certificate: , not readable, 0 bytes
Key: , not readable, 0 bytes
Ciphers: NORMAL
Creds:

Hooks
Scripts: Enabled
/home/saukrs/.task/hooks/on-modify.timewarrior (executable)

Tests
$TERM: xterm-color (324x71)
Dups: Scanned 565 tasks for duplicate UUIDs:
No duplicates found
```