bug: fix ibc transfer from ethermint to external chain

[dudong2]

Closes: #XXX

Description

• Fixes an issue that caused a nil pointer error when doing an ibc transfer to an external chain because the ibc's transfer keeper had an ics4 wrapper of nil when it was created.

how to test

• check that ibc transfer from canto to external chain is performed well without panic

ref. b-harvest/Canto#71

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.30%. Comparing base (0712f94) to head (6d675de).

Additional details and impacted files

@@                Coverage Diff                @@
##           canto-v8/develop      #11   +/-   ##
=================================================
  Coverage             68.30%   68.30%           
=================================================
  Files                   117      117           
  Lines                 11240    11240           
=================================================
  Hits                   7677     7677           
  Misses                 3088     3088           
  Partials                475      475           

Files	Coverage Δ
app/app.go	85.27% <100.00%> (ø)

[poorphd]

LGTM