Error if Positional Params num is zero

[mmisono]

Positional parameter zero ($0) is invalid. Previously, using $0 causes
std::out_of_range error due to the underflow and confuses users.

% sudo ./src/bpftrace -e 'k:$0 {}' vfs_open
terminate called after throwing an instance of 'std::out_of_range'
  what():  vector::_M_range_check: __n (which is 18446744073709551615) >= this->size() (which is 1)
zsh: abort      sudo ./src/bpftrace -e 'k:$0 {}' vfs_open

This commit changes this and in the parser check the positional params
num is not zero. This can be also done in the lexical analyzer, but to
print verbose an error message do this in the parser. Now the error message is

% sudo ./src/bpftrace -e 'k:$0 {}' vfs_open
stdin:1:1-5: ERROR: param $0 is out of integer range [1, 9223372036854775807]
k:$0 {}
~~~

Checklist

• Language changes are updated in docs/reference_guide.md
• User-visible and non-trivial changes updated in CHANGELOG.md
• The new behaviour is covered by tests

[mmisono]

@fbs
Is It OK to merge this? My fixes' CHANGELOG would conflict, so I'll fix it one by one.