Fixes die on not defined arrays throw a up_var without key or index in 1.10_02

[Patrick Hochstenbach]

Fixes die when array paths don't exist

$ catmandu convert Null to YAML --fix 'upcase(text.0)'
--- {}
...
$ catmandu convert Null to YAML --fix 'upcase(demo.0)'
Oops! up_var without key or index

[Nicolas Steenlant]

fixed in 1.10_03