fix: Fix double shim creating when non-empty sbin'' ice.

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Currently, e.g. following command:

zi sbin'dstask*->tsk' bpick'dstask-linux-amd*' ghapi from'gh-r' for dstask

Will create two shims, tsk and 'dstask-linux-amd64'.

Description

An unconditional iteration over "" shim with:

for sbin ( $sbins "" )

has been changed to conditional iteration with:

(( !$#sbins )) && sbins+=("")

Motivation and Context

To create shims correctly without extra one.

Related Issue(s)

21

Usage examples

No unscope annex example:

zi sbin'dstask*->tsk' bpick'dstask-linux-amd*' from'gh-r' for naggie/dstask

How Has This Been Tested?

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

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Difference, before:

After:

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@vladdoster when merged?