sh: Fix two issues when an alias is redefined:
sh: Fix two issues when an alias is redefined:

 * The last character is not displayed.
 * If the alias ends with itself (as a word), an infinite memory-eating loop
   occurs.

If an alias is defined initially, a space is appended to avoid recursion but
this did not happen when an alias was later modified.

PR:		bin/173418
Submitted by:	Daniel F.
MFC after:	1 week

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