Report named 'tasks' breaks all subcommands

If my `.taskrc` defines a report named `tasks` this completely breaks all subcommands and causes any arguments to `task` to be interpreted as a filter. This is very bizarre.

For context, I used to use taskwarrior years ago, and I had a `.taskrc` set up that, among other things, included the following definition:

```
report.tasks.description=List all pending tasks by age
report.tasks.columns=id,project,priority,entry.age,start.age,due.countdown,depends,issue,issuepriority,tags,description
report.tasks.filter=status:pending
report.tasks.labels=ID,Proj,Pri,Age,Sta,Due,Deps,Issue,Pri,Tags,Description
report.tasks.sort=entry+
```

With this in place, `task` with no arguments will ignore the default command and print all tasks, and any arguments are just interpreted as a filter on that. So for example `task help` just shows me all tasks whose description or notes includes the word "help" somewhere.

### `task diag`

With the above report intact, `task diag` just tells me "No matches", but after commenting out that report I get the following:

```
task 2.5.1
Platform: Darwin

Compiler
Version: 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.37)
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
Built: Oct 10 2017 23:38:24
CMake: 3.9.4
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.5.15
Build type: Release

Configuration
File: /Users/kevin/.taskrc (found), 3389 bytes, mode 100644
Data: /Users/kevin/Dropbox/.task (found), dir, mode 40755
Locking: Enabled
GC: Enabled
rc.editor: vim
Server:
Trust: strict
Certificate: , not readable, 0 bytes
Key: , not readable, 0 bytes
Ciphers: NORMAL
Creds:

Hooks
System: Enabled
Location: /Users/kevin/Dropbox/.task/hooks
(-none-)

Tests
$TERM: xterm-256color (120x25)
Dups: Scanned 446 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 446 tasks for broken references:
No broken references found

```