Using re: in the description creates and recurring task with empty interval

#### To report a bug...

* What command(s) did you run?
```task next```

* What did you expect to happen?
I'd be presented with my list of to-do items from the next report.

* What actually happened?
Received the following output:
```The recurrence value '' is not valid.```
No report output.

I tried a few additional things to see if I could get my list of tasks back ...
* I restored from my backup from a working day a couple days ago, ran task and received the same error.
* I figured out, however, if I changed my system clock back to yesterday's date, however, that ```task next``` just fine.
* I tried setting the date forward to tomorrow, to see if time will just sort of fix this error on it's own, and unfortunately it's still generating the same error/behavior.
* I have yet to be able to determine which recurring task in my data is causing this to happen, especially since the value is presented as, apparently, a null string.

* Paste the output of the ```task diag``` command.
```
task 2.5.1
Platform: FreeBSD

Compiler
Version: 4.2.1 Compatible FreeBSD Clang 8.0.0 (tags/RELEASE_800/final 356365)
Caps: +stdc +stdc_hosted +ILP32 +c8 +i32 +l32 +vp32 +time_t64
Compliance: C++11

Build Features
Built: Jan 12 2020 02:09:36
CMake: 3.15.5
libuuid: libuuid, no uuid_unparse_lower
libgnutls: 3.6.11
Build type: Release

Configuration
File: /home/mercadal/.taskrc (found), 1648 bytes, mode 100644
Data: /home/mercadal/.task (found), dir, mode 40755
Locking: Enabled
GC: Enabled
$EDITOR: vi
Server:
Trust: strict
Certificate: , not readable, 0 bytes
Key: , not readable, 0 bytes
Ciphers: NORMAL
Creds:

Hooks
System: Enabled
Location: /home/mercadal/.task/hooks
(-none-)

Tests
$TERM: xterm (175x62)
Dups: Scanned 375 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 375 tasks for broken references:
No broken references found
```